Math

Most used

• High School GPA CalculatorWeighted high-school GPA from your grade points, credits and the credits you took in honors and AP courses, with the boost set to your school's policy.
• SAT Score CalculatorAdd your Math and Reading & Writing section scores to get the total SAT score out of 1600.
• AP US Government Score CalculatorPredict your AP US Government score from your multiple-choice count and the four free-response scores.
• Square Feet to Linear Feet CalculatorTurn an area into a running length of material once you know how wide the boards or rolls are.
• Percentage to GPA CalculatorConvert a percentage, an Indian 10-point CGPA or a German grade into a GPA on the 4.0 scale.
• German Abitur Grade Calculator (KMK Scale)Turn an exam percentage or raw points into Notenpunkte on the 15-point KMK scale used in the German Abitur.
• AP Calc AB Score Calculator (US Exam)Predict your 1–5 score on the US AP Calculus AB exam from your multiple-choice count and your free-response points.
• Fraction CalculatorAdd, subtract, multiply or divide two fractions and read the result as a decimal.
• Percentage CalculatorCalculate a percentage of a number, a percentage share or an increase or decrease. Enter your values and see the formula with worked examples.
• AP Chem Score Calculator (US Exam)Turn your raw multiple-choice and free-response scores from the US AP Chemistry exam into a predicted 1–5 score.
• AP Psych Score Calculator (US Exam)Turn your multiple-choice count and your AAQ and EBQ rubric scores from the US AP Psychology exam into a predicted 1–5 score.
• AP Stats Score Calculator (US Exam)Turn your multiple-choice count, your five free-response scores and the investigative task from the US AP Statistics exam into a 1–5 score.
• Decimal to Fraction ConverterTurn a decimal into its simplest fraction. 0.375 gives 3/8, and a repeating 0.3333 gives 1/3 rather than 3333/10000.
• Final Grade CalculatorWhat you need to score in the final exam to reach the course grade you are aiming for.
• Pipe Weight CalculatorWeight of a pipe run from outside diameter, wall thickness, length and material.

All, A–Z

• #
• 2×2 System of EquationsSolve two linear equations in two unknowns by Cramer's rule — enter the six coefficients and get x and y.
• 3D Distance CalculatorThe straight-line distance between two points in space, from their x, y and z coordinates.
• A
• Absolute Humidity CalculatorWater vapour in grams per cubic metre, from the air temperature and the relative humidity.
• Acceleration ConverterConvert m/s², ft/s², g, galileo, km/h/s and mph/s with exact factors, in either direction.
• ACT Score Calculator (US College Entrance Test)Average your four ACT section scores — English, math, reading and science — into the composite from 1 to 36, rounded the way ACT rounds it.
• Air Density CalculatorDensity of dry air in kilograms per cubic metre, from absolute pressure and temperature in kelvin.
• Air Pressure at Altitude CalculatorAtmospheric pressure at a given height above sea level, from the standard barometric formula.
• Amps to Watts CalculatorPower in watts from current in amps and voltage, using Watt's law P = V × I.
• Angle Between Vectors CalculatorThe angle between two 3D vectors in degrees, from the dot product and the two magnitudes.
• Angle ConverterConvert degrees, radians, gon, arcminutes, arcseconds and full turns with exact factors, in either direction.
• Angular Acceleration CalculatorAngular acceleration in rad/s² from a starting and a final angular velocity in rad/s and the time the change took.
• Angular Frequency CalculatorAngular frequency ω from an ordinary frequency in hertz — one full cycle is 2π radians.
• Angular Momentum CalculatorAngular momentum of a point mass on a circular path in kg·m²/s, from its mass, its tangential speed and its radius.
• Angular Size CalculatorHow wide an object looks from a given distance, in degrees — the small-angle approximation.
• Annular Sector Area CalculatorThe area of a ring sector from the inner radius, the outer radius and the opening angle.
• Annulus Area CalculatorThe area of a ring between two concentric circles, from the outer and inner radius.
• Antenna Length CalculatorHalf-wave dipole length in metres from a frequency in MHz and a velocity factor — λ = c / f, then times the factor, then halved.
• AP Lang Score Calculator (US Exam)Turn raw multiple-choice and essay points from the US AP English Language exam into an estimated 1–5 score on a 100-point composite.
• AP Physics 1 Score Calculator (US Exam)Turn raw multiple-choice and free-response points from the 2025 US AP Physics 1 exam into an estimated 1–5 score on a 100-point composite.
• Apparent Brightness CalculatorRadiant flux reaching an observer from a point source — luminosity spread over a sphere.
• Arc Length CalculatorThe length of a circular arc from the radius and the angle it spans, in degrees.
• Area ConverterConvert square metres, hectares, square feet, square yards, acres and square miles with exact factors, in either direction.
• Arithmetic Sequence CalculatorThe nth term of an arithmetic sequence from its first term, common difference and position — with the sum of the first n terms.
• Arrhenius Equation CalculatorReaction rate constant k = A · exp(−Ea / (R · T)) from the pre-exponential factor, the activation energy in J/mol and the temperature in kelvin.
• Aspect Ratio CalculatorAspect ratio of any pixel size as a decimal — width divided by height, with the reduced whole-number ratio alongside.
• Average Acceleration CalculatorThe average acceleration from a starting velocity, an ending velocity and the time between them — the change in velocity over the time.
• B
• Banked Curve Angle CalculatorThe ideal banking angle of a curve — the tilt at which no tyre friction is needed at a given speed and radius.
• Battery Life CalculatorRuntime in hours from battery capacity in mAh and the current the device draws in mA.
• Beat Frequency CalculatorHow fast two tones beat against each other — the absolute difference of their frequencies.
• Beer-Lambert Law CalculatorAbsorbance from molar absorptivity, concentration and path length — A equals ε times c times l.
• Belt Length CalculatorThe length of an open belt around two pulleys from the centre distance and both pulley diameters.
• Boiling Point Elevation CalculatorHow much higher a solution boils than the pure solvent: ΔTb = i × Kb × b, from the van 't Hoff factor, Kb and the molality.
• Box Diagonal CalculatorThe space diagonal of a rectangular box from its length, width and height.
• Boyle's Law CalculatorThe new pressure of a gas after its volume changes at constant temperature: p₁V₁ = p₂V₂.
• Buoyancy Force CalculatorThe upward buoyant force on a submerged or floating body from the fluid density and the volume it displaces.
• C
• Capacitance CalculatorCapacitance in farads from the stored charge in coulombs and the voltage across the plates.
• Capacitive Reactance CalculatorCapacitive reactance Xc in ohms from frequency and capacitance, using Xc = 1 ÷ (2πfC).
• Capacitor Charge CalculatorCharge stored in a capacitor in coulombs, from its capacitance and the voltage across it.
• Capacitor Energy CalculatorThe energy stored in a charged capacitor, E = ½CV², in joules from its capacitance and voltage.
• Carnot Efficiency CalculatorThe highest efficiency any heat engine can reach between two temperatures, both in kelvin.
• Center of Mass CalculatorThe balance point of two masses on a line, from their masses in kilograms and their positions along one axis.
• Centripetal Acceleration CalculatorThe inward acceleration of an object moving in a circle, a = v² ÷ r, in metres per second squared from its speed and the radius.
• Centripetal Force CalculatorThe inward force that keeps an object on a circular path, F = m × v² ÷ r, in newtons from its mass, speed and radius.
• Charles's Law CalculatorThe new volume of a gas after a temperature change at constant pressure: V₁/T₁ = V₂/T₂.
• Circle Area CalculatorThe area of a circle from its radius, with the circumference and diameter alongside.
• Circular Segment Area CalculatorThe area of a circular segment — the piece cut off by a chord — from the radius and angle.
• Cloud Base CalculatorThe height of the convective cloud base above ground, from the surface temperature and dew point.
• Coefficient of Restitution CalculatorHow bouncy a collision is, from a drop test — the square root of the bounce height divided by the drop height.
• Coil Inductance CalculatorInductance of a single-layer air-core coil in µH, from its turns, radius and length.
• Collatz Steps CalculatorHow many 3n + 1 steps a starting number needs to reach 1 — 27 takes 111 of them and climbs to 9232 along the way.
• Combined Gas Law CalculatorThe new volume of a gas when pressure and temperature both change: p₁V₁/T₁ = p₂V₂/T₂.
• Complex Number Modulus CalculatorThe modulus |z| of a complex number a + bi — its distance from the origin — with the argument in degrees alongside.
• Cone Surface Area CalculatorThe total surface area of a right circular cone from its base radius and slant height.
• Cone Volume CalculatorThe volume of a right circular cone from its base radius and vertical height.
• Continuity Equation CalculatorDownstream velocity of an incompressible fluid from the upstream area, the upstream velocity and the downstream area.
• Coulomb's Law CalculatorThe electrostatic force between two point charges from their size and separation — F = kₑ|q₁q₂| ÷ r².
• Cross Product Magnitude CalculatorThe length of A × B for two 3D vectors — the area of the parallelogram the two vectors span.
• Cube Volume CalculatorThe volume of a cube from one edge, with the surface area and both diagonals alongside.
• Cuboid Surface Area CalculatorTotal surface area of a rectangular box from length, width and height — six faces in three matching pairs.
• Current Divider CalculatorCurrent through one of two parallel resistors, from the total current and both resistances.
• Cylinder Surface Area CalculatorThe total surface area of a cylinder from its radius and height, both circular ends included.
• Cylinder Volume CalculatorThe volume of a cylinder from its base radius and height — π times the radius squared times the height.
• Cylindrical Shell Volume CalculatorThe volume of a pipe wall — outer cylinder minus bore — from both radii and the height.
• D
• Data Size ConverterConvert between bits, bytes, KB, MB, GB, TB and the binary KiB, MiB, GiB, TiB.
• Data Transfer Rate ConverterConvert Mbit/s, Gbit/s, MB/s and the rest — and see why 100 Mbit/s is only 12.5 MB/s.
• dBm to Watts CalculatorConvert a power level in dBm to watts and milliwatts. 0 dBm is 1 mW, 30 dBm is 1 W, and every 10 dB is a factor of ten.
• dBW to Watts CalculatorConvert a power level in dBW to watts. 0 dBW is 1 W, 30 dBW is 1 kW, and dBm is always the same figure plus 30.
• De Broglie Wavelength CalculatorMatter wavelength of a moving particle, λ = h / (m × v), in nanometres — from its mass in kg and its speed.
• Decay Constant CalculatorThe radioactive decay constant λ from a half-life — λ = ln(2) divided by the half-life.
• Decibel CalculatorThe decibel difference between two powers — ten times the base-ten log of their ratio.
• Decibel Gain CalculatorVoltage gain in decibels — twenty times the base-ten log of output over input.
• Decibel Sum CalculatorTwo sound levels combined — decibels add through their intensities, not directly.
• Density CalculatorDensity in kilograms per cubic metre from a mass in kilograms and a volume in cubic metres.
• Dew Point CalculatorThe dew point in °C from air temperature and relative humidity, using the Magnus formula.
• Dilution Ratio CalculatorHow much concentrate and water a ratio like 1:10 needs for a target volume — read as 1 part to 10 parts, so 11 in total.
• Discount CalculatorWhat you pay after a discount, and how much comes off — from the full price and the percentage off.
• Distance Between Two PointsThe straight-line distance between two points in the plane, from their x and y coordinates.
• Distance from a Point to a LineThe perpendicular distance from a point to a line written as a·x + b·y + c = 0.
• Divisor Count CalculatorHow many positive divisors a whole number has — τ(n) — with their sum σ(n) beside it, for spotting primes and perfect numbers.
• Doppler Effect CalculatorObserved frequency of a moving sound source for a stationary listener — the pitch shift of a passing siren.
• Dot Product CalculatorThe scalar product of two 3D vectors — matching components multiplied and added, one number as the answer.
• Doubling Time CalculatorHow long a quantity growing at a constant rate takes to double — t = ln(2) divided by the rate.
• Drag Force CalculatorAerodynamic drag from fluid density, speed, drag coefficient and frontal area — F = ½ρv²CdA.
• E
• Efficiency CalculatorEfficiency as a percentage from the useful output and the total input you put in.
• Electric Charge CalculatorThe charge in coulombs that a steady current carries in a given time — Q = I × t.
• Electric Field CalculatorThe uniform field between two parallel plates, from the voltage across them and the gap — E = V ÷ d.
• Electricity Cost CalculatorWhat an appliance costs to run per day, from its wattage, its daily run time and your price per kilowatt-hour.
• Ellipse Area CalculatorThe area of an ellipse from its two semi-axes — π times their product.
• Ellipse Eccentricity CalculatorThe eccentricity of an ellipse from its semi-major and semi-minor axis.
• Ellipse Perimeter CalculatorThe perimeter of an ellipse from its semi-major and semi-minor axis, by Ramanujan's formula.
• Ellipsoid Volume CalculatorVolume of an ellipsoid from its three semi-axes — a squashed or stretched sphere, egg, rugby ball or watermelon.
• Energy ConverterConvert energy between joule, kilojoule, calorie, kilocalorie, watt-hour, kilowatt-hour, BTU and foot-pound.
• Engineering Notation ConverterConvert a decimal number into engineering notation — a coefficient from 1 to 1000 times a power of ten that is a multiple of three.
• Equation of a LineThe equation of the straight line through two points, in slope-intercept form y = mx + b.
• Equilateral Triangle CalculatorThe area of an equilateral triangle from its side length, plus height and perimeter.
• Error Quotient CalculatorWork out the German Fehlerquotient — errors per hundred words — and compare it against the published Hessen thresholds.
• Escape Velocity CalculatorEscape velocity of a celestial body from its mass and radius, v = √(2GM/r), in metres per second.
• Exponent CalculatorRaise any base to any power — whole, negative or fractional exponents included.
• Exponential Growth CalculatorContinuous exponential growth A = P · e^(r·t) — the amount after a number of periods at a constant rate.
• Exposure Value CalculatorExposure value in stops from an aperture f-number and a shutter speed in seconds, on the base-2 photographic scale.
• F
• F-Stop CalculatorThe f-number of a lens from its focal length and the diameter of its entrance pupil, both in millimetres.
• Factorial Calculatorn! — the product of every whole number up to n, and the count of its orderings.
• Fibonacci CalculatorThe nth Fibonacci number, counted from F(0) = 0 and F(1) = 1 up to F(78).
• Flywheel Energy CalculatorThe rotational energy stored in a spinning flywheel, in joules, from its moment of inertia and its angular velocity in rad/s.
• Foot-Candles to Lux ConverterIlluminance in lux from a reading in foot-candles, using the exact factor 1 fc = 10.7639 lx.
• Force ConverterConvert newtons, kilonewtons, dyne, kilogram-force, gram-force, pound-force and ounce-force with exact factors.
• Free Fall Distance CalculatorHow far an object falls in a given time under gravity alone, with air resistance ignored.
• Freezing Point Depression CalculatorHow much lower a solution freezes than the pure solvent: ΔTf = i × Kf × b, from the van 't Hoff factor, Kf and the molality.
• Frequency ConverterConvert frequency between hertz, kilohertz, megahertz, gigahertz, terahertz and revolutions per minute.
• Frequency to Period CalculatorTurn a frequency in hertz into the period of one cycle in seconds — T = 1 / f, the plainest reciprocal in electronics.
• Friction Force CalculatorThe friction force between two surfaces from the coefficient of friction and the normal force pressing them together.
• Frustum Surface Area CalculatorThe total surface area of a conical frustum from both radii and the vertical height.
• Frustum Volume CalculatorThe volume of a conical frustum — a cone with the tip cut off — from both radii and the height.
• Fuel Economy ConverterConvert between L/100 km, MPG (US), MPG (UK) and km/L — an inverse, not a factor.
• G
• G-Force CalculatorConvert an acceleration in m/s² into g-force — the same acceleration as a multiple of standard gravity.
• GCF Calculator — Greatest Common FactorThe greatest common factor of two whole numbers by Euclid's algorithm, with the least common multiple that follows from it in one step.
• Gear Ratio CalculatorThe ratio of a gear pair from the two tooth counts — driven teeth divided by driver teeth.
• Geometric Mean of Two NumbersThe geometric mean of two positive numbers, √(a × b) — the right average for ratios and growth factors, with the arithmetic mean beside it.
• Geometric Sequence CalculatorThe nth term of a geometric sequence from its first term, common ratio and position — with the sum of the first n terms.
• German Grade Scale Calculator (Linear Key)Turn exam points into a German grade from 1.0 to 6.0 with the linear key: grade = 6 − 5 × points ÷ maximum.
• Gibbs Free Energy CalculatorThe change in Gibbs free energy, ΔG = ΔH − T·ΔS, in J/mol — from a reaction's enthalpy change, absolute temperature and entropy change.
• Glass Weight CalculatorWeight of a pane from its length, width, thickness and material — glass, acrylic or polycarbonate.
• Golden Ratio CalculatorSplit a length in the golden ratio φ ≈ 1.618. The answer is the longer part; the shorter part is whatever is left of the total.
• GPA CalculatorYour GPA from total grade points and total credits on the 4.0 scale, with an optional prior record for the cumulative GPA.
• Grade Curve CalculatorFour common grading curves — flat bump, square root, scale to top score and a plain multiplier — applied to one raw score.
• Grade Points Calculator (0–15)Convert German upper-school grade points (0–15) into the classical mark 1–6 with its decimal tendency, on the KMK scale.
• Gravitational Force CalculatorNewton's law of universal gravitation — the attraction between two masses from their sizes and the distance between their centres.
• H
• Half-Life CalculatorWhat percentage of a substance is still present after a given time — from its half-life alone.
• Harmonic Mean of Two NumbersThe harmonic mean of two positive numbers, 2ab ÷ (a + b) — the correct average for speeds and rates over equal distances.
• Haversine Distance CalculatorGreat-circle distance between two coordinates — the as-the-crow-flies kilometres over the Earth's surface.
• Heat Capacity CalculatorThe heat capacity of a whole object in J/K, from the heat energy added and the temperature rise it caused.
• Heat Conduction CalculatorSteady-state heat flow through a flat layer in watts, by Fourier's law — conductivity, area, temperature difference and thickness.
• Heat Energy CalculatorHeat energy in joules from a mass, its specific heat capacity, and the temperature change.
• Heat Index CalculatorThe NWS feels-like heat index in °F from the shade air temperature and the relative humidity.
• Height Converter — Centimetres to InchesConvert a height in centimetres to inches. One inch is exactly 2.54 cm, so the inch value is exact — the feet-and-inches reading is in the table.
• Hemisphere Volume CalculatorThe volume of a half sphere from its radius — two thirds of π times the radius cubed.
• Henderson-Hasselbalch CalculatorBuffer pH from the pKa and the concentrations of the conjugate base and the weak acid.
• Heron's Formula CalculatorThe area of a triangle from its three sides alone — Heron's formula, no height and no angles needed.
• Hexagon CalculatorThe area of a regular hexagon from its side length, plus perimeter, apothem and diagonals.
• Hexagonal Prism Volume CalculatorThe volume of a regular hexagonal prism from one side of the hexagon and the length of the bar.
• Hooke's Law CalculatorSpring force from the spring constant and the displacement — F = k × x, the magnitude of the restoring force.
• Hubble's Law CalculatorDistance to a receding galaxy in megaparsecs — recession velocity divided by the Hubble constant you choose.
• Humidex CalculatorCanada's humidex comfort index from the air temperature and the dew point, both in °C.
• Hydrostatic Pressure CalculatorGauge pressure of a fluid column from its density and depth, with standard gravity — P = ρgh in pascals.
• I
• Ideal Gas Law CalculatorMoles of gas from pressure, volume and temperature using pV = nRT with the exact gas constant.
• IHK Grading Scale CalculatorConvert exam points into the German IHK grade 1 to 6 using the published 100-point key: 92, 81, 67, 50 and 30 points.
• Impact Force CalculatorThe average force of a collision from the mass, the speed at impact and the distance over which the object stops.
• Impedance CalculatorThe magnitude of a series RLC impedance in ohms, from the resistance and the net reactance.
• Impulse CalculatorThe impulse of a constant force over a time interval, J = F × Δt, in newton-seconds — which equals the change in momentum.
• Inductive Reactance CalculatorInductive reactance XL in ohms from frequency and inductance, using XL = 2πfL.
• Inductor Energy CalculatorThe energy stored in an inductor's magnetic field, E = ½LI², in joules from inductance and current.
• Initial Bearing CalculatorThe compass bearing from one coordinate to another — the forward azimuth in degrees from true North.
• Inverse Square Law CalculatorIntensity of a point source at a new distance, from a known reading at a reference distance.
• Isosceles Triangle CalculatorArea, height, perimeter, base angle and apex angle of an isosceles triangle from its base and equal leg.
• K
• Kinetic Energy CalculatorThe kinetic energy of a moving object in joules, from its mass in kilograms and its speed in metres per second.
• Kite Area CalculatorThe area of a kite from its two diagonals — area = ½ × p × q, no side lengths required.
• Knick Grading Scale CalculatorGrade a test with a bent German key: the pass mark you choose anchors grade 4, four steps run above it and two below.
• kVA to kW CalculatorConvert apparent power in kVA to real power in kW using the power factor of the load.
• kW to kVA CalculatorConvert real power in kW to apparent power in kVA using the power factor — for sizing generators and UPS units.
• L
• Latent Heat CalculatorThe heat absorbed or released by a phase change in joules, from the mass and the specific latent heat of the substance.
• Law of Cosines CalculatorThe third side of a triangle from two sides and the angle between them — c = √(a² + b² − 2ab·cos C).
• Law of Sines CalculatorAn unknown side of a triangle from one side, its opposite angle and a second angle — b = a × sin B ÷ sin A.
• LC Resonant Frequency CalculatorThe resonant frequency of an LC circuit, f = 1 ÷ (2π√(LC)), in hertz from inductance and capacitance.
• Lead Time CalculatorTotal supply-chain lead time in days — order processing plus production plus transit, on one consistent basis.
• LED Resistor CalculatorThe series resistor an LED needs, from the supply voltage, its forward voltage and the target current.
• Length ConverterConvert millimetres, metres, kilometres, inches, feet, yards, miles and nautical miles with exact factors, in either direction.
• Lever CalculatorThe effort force a lever needs, from the load and the two arm lengths — the law of the lever in newtons.
• Linear Interpolation CalculatorThe value y at any x on the straight line through two known points — interpolation inside the pair, extrapolation outside it.
• Logarithm CalculatorThe logarithm of any positive number to any base, with the natural logarithm ln alongside it for comparison.
• Lorentz Factor CalculatorThe Lorentz factor gamma of special relativity from a speed in metres per second — how far time, length and mass are stretched.
• Lorentz Force CalculatorMagnetic force on a moving charge — F = q × v × B, for a charge travelling perpendicular to the field.
• Lumens to Lux CalculatorIlluminance in lux from the luminous flux of a lamp in lumens and the area it has to cover.
• Lumens to Watts CalculatorPower draw in watts for a target brightness in lumens, from the lamp's luminous efficacy in lm/W.
• Luminosity CalculatorStellar luminosity in solar luminosities from a star's radius in metres and its surface temperature.
• Lux to Foot-Candles ConverterIlluminance in foot-candles from a reading in lux, using the exact factor 1 fc = 10.7639 lx.
• Lux to Lumens CalculatorTotal luminous flux in lumens from a target illuminance in lux and the area you want to light.
• M
• Mach Number CalculatorMach number from an object's speed and the local speed of sound — subsonic, supersonic or hypersonic.
• Magnetic Flux CalculatorMagnetic flux in webers from the field strength and the area it passes through — Φ = B × A for a perpendicular field.
• Magnetic Force on a Wire CalculatorForce on a current-carrying wire in a magnetic field — F = B × I × L, for a current running perpendicular to the field.
• Magnification CalculatorLinear magnification from image height and object height — a plain ratio, with no unit of its own.
• mAh to Wh CalculatorBattery capacity in mAh converted to energy in watt-hours using the nominal pack voltage.
• Markup CalculatorThe selling price and profit from a cost and a markup percentage — markup measured against cost, not price.
• Mass Flow Rate CalculatorMass flow rate in kilograms per second from the fluid density, the cross-sectional area and the flow velocity.
• Mass-Energy Equivalence CalculatorThe rest energy of a mass from Einstein's E = mc², in joules, using the exactly defined speed of light c = 299792458 m/s.
• Mechanical Advantage CalculatorHow many times a lever, pulley or ramp multiplies your force, from load and effort.
• mg to ml ConverterConvert milligrams to millilitres and back, using the concentration in mg per ml.
• Midpoint CalculatorFind the midpoint of the segment between two points — ((x1 + x2) / 2, (y1 + y2) / 2), the exact centre halfway between them.
• Modulo Calculatora mod n — the remainder after division — in the floored convention, so the remainder always carries the sign of the divisor.
• Molality CalculatorMolality b = moles of solute ÷ kilograms of solvent, in mol/kg — the temperature-independent counterpart of molarity.
• Molarity CalculatorMolar concentration in mol/L from the moles of solute and the volume of the finished solution in litres.
• Mole Fraction CalculatorThe mole fraction of component A in a two-part mixture: x_A = nA ÷ (nA + nB), a dimensionless number between 0 and 1.
• Moles CalculatorAmount of substance in moles from a mass in grams and the molar mass in g/mol.
• Moment of Inertia of a Point MassMoment of inertia of a point mass — or a thin ring about its own axis — in kg·m², from the mass and its distance to the axis.
• Momentum CalculatorLinear momentum in kilogram-metres per second, from an object's mass in kilograms and its speed in metres per second.
• N
• NE555 Astable CalculatorOutput frequency of a 555 timer running free in astable mode, from R1, R2 and the timing capacitor in microfarads.
• NE555 Monostable CalculatorOutput pulse width of a 555 timer in monostable (one-shot) mode, from the timing resistor in ohms and the capacitor in microfarads.
• Newton's Second Law CalculatorThe net force on an object from its mass and acceleration, F = m × a, in newtons — Newton's second law of motion.
• Nth Root CalculatorThe nth root of a number, from square and cube roots up to any higher degree — ⁿ√x = x^(1/n).
• O
• Octagon Area CalculatorThe area of a regular octagon from its side length, with perimeter, apothem and circumradius alongside.
• Octagonal Prism Volume CalculatorThe volume of a regular octagonal prism from one side of the octagon and the length of the bar.
• Ohm's LawSolve for voltage, current, resistance or power. Pick the quantity you need and enter the two you already know.
• Orbital Period CalculatorKepler's third law — the time for one full orbit from the semi-major axis and the central mass, in seconds.
• Orbital Velocity CalculatorCircular orbital velocity from the central mass and the orbital radius, v = √(GM/r), in metres per second.
• Orifice Flow Rate CalculatorFlow rate through an orifice from the discharge coefficient, the opening area, the head above it and gravity.
• Osmotic Pressure CalculatorOsmotic pressure in atmospheres from the van 't Hoff equation Π = i × M × R × T, with the temperature in kelvin.
• P
• Parallax Distance CalculatorDistance to a star in parsecs from its annual parallax angle — one divided by the angle in arcseconds.
• Parallel Axis Theorem CalculatorMoment of inertia about a shifted axis: the centre-of-mass value plus mass times the square of the distance between the two axes.
• Parallel Capacitance CalculatorThe total capacitance of two capacitors in parallel, where the values simply add: C = C1 + C2.
• Parallel Inductance CalculatorThe equivalent inductance of two coils in parallel — the product over the sum, in henries.
• Parallel Resistor CalculatorThe combined resistance of two resistors in parallel, by the product-over-sum rule Rp = R1R2 ÷ (R1 + R2).
• Parallel-Plate Capacitor CalculatorCapacitance of a parallel-plate capacitor in picofarads, from plate area, gap and dielectric constant.
• Parallelogram Area CalculatorThe area of a parallelogram from its base and the perpendicular height between the two parallel sides.
• Partial Pressure CalculatorThe partial pressure of one gas in a mixture: mole fraction × total pressure, in the pressure unit you entered.
• Pascal's Principle CalculatorOutput force of a hydraulic press from the input force and the two piston areas — F₂ = F₁ × A₂ ÷ A₁.
• Pay Raise CalculatorYour new pay and the size of the increase from a raise percentage — hourly, monthly or annual, and pay cuts too.
• Pendulum Period CalculatorThe period of a simple pendulum from its length — one full swing, over and back, in seconds.
• Pentagon Area CalculatorThe area of a regular pentagon from its side length, with perimeter, apothem and circumradius alongside.
• Pentagonal Prism Volume CalculatorThe volume of a regular pentagonal prism from one side of the pentagon and the length of the bar.
• Percent Error CalculatorHow far a measured value sits from the accepted true value, as a percentage of that true value.
• Percent Yield CalculatorPercent yield = actual yield ÷ theoretical yield × 100, with both amounts in the same unit.
• Percentage Change CalculatorCalculate the percentage increase or decrease between an old and a new value. Enter your numbers and check the formula and worked examples.
• Percentage Difference CalculatorThe gap between two equally valid values as a percentage of their average — symmetric, so the order never matters.
• pH CalculatorThe pH of an aqueous solution from its hydrogen-ion concentration in mol/L.
• Photon Energy CalculatorEnergy of a single photon in electronvolts from its wavelength in metres, using the exact SI values of h and c.
• Photon Momentum CalculatorMomentum of a photon from its wavelength, p = h / λ, with the exact CODATA Planck constant. Answer in units of 10⁻²⁷ kg·m/s.
• Pixels to Inches ConverterConvert between pixels, inches, centimetres, millimetres and points at any resolution.
• Polar to Rectangular ConverterConvert a point between polar and rectangular coordinates in either direction, in degrees or radians, with a quadrant-correct angle.
• Polygon Interior Angle CalculatorEach interior angle of a regular polygon and the sum of all interior angles, from the number of sides.
• Potential Energy CalculatorThe gravitational potential energy of a raised object, E = m × g × h with g = 9.80665 m/s², in joules from its mass and height.
• Power Calculator (Work ÷ Time)Mechanical power in watts from the work done in joules and the time it took in seconds — one watt is one joule per second.
• Power ConverterConvert power between watt, kilowatt, megawatt, mechanical horsepower, metric horsepower (PS) and BTU per hour.
• Power Dissipation CalculatorThe heat a resistor gives off, from the current through it and its resistance — P = I² × R in watts.
• Power Factor CalculatorThe power factor of an AC circuit from its real power in watts and its apparent power in volt-amperes.
• Power-to-Weight Ratio CalculatorWatts per kilogram from any power and weight units, with horsepower per tonne and per pound alongside.
• PPI CalculatorPixel density of a display from its resolution and diagonal: the pixel diagonal divided by the diagonal in inches.
• PPM CalculatorParts per million by mass: ppm = mass of solute ÷ mass of solution × 1,000,000. Both masses in the same unit.
• Pressure CalculatorPressure in pascals from a force in newtons spread over an area in square metres.
• Pressure ConverterConvert pressure between pascal, hectopascal, kilopascal, bar, millibar, atmosphere, psi, mmHg and inHg.
• Price Elasticity of Demand CalculatorPrice elasticity of demand by the midpoint (arc) method, from two prices and two quantities — signed, so a normal good comes out negative.
• Prime Factorization CalculatorBreak any whole number from 2 to a billion into its prime factors in exponent form — 360 becomes 2^3 × 3^2 × 5.
• Profit Margin CalculatorProfit margin from a cost and a selling price — profit measured against the price, with markup shown alongside.
• Projectile Maximum Height CalculatorThe peak height of a projectile from its launch speed and angle, on level ground with no air resistance.
• Projectile Range CalculatorHow far a projectile flies from its launch speed and angle, on level ground with no air resistance.
• Projectile Time of Flight CalculatorHow long a projectile stays in the air, from its launch speed, launch angle, and the local gravity.
• Proportion Calculator (Rule of Three)Solve the missing fourth value in A : B = C : x by cross-multiplication, or switch to inverse proportion when one quantity falls as the other rises.
• Pyramid Frustum Volume CalculatorVolume of a square pyramid frustum from its bottom side, top side and height, with slant height and surfaces beside it.
• Pyramid Surface Area CalculatorTotal surface area of a right square pyramid from its base edge and slant height, with the lateral area beside it.
• Pyramid Volume CalculatorThe volume of a square pyramid from its base edge and vertical height.
• Pythagorean Theorem CalculatorThe hypotenuse of a right triangle from its two legs — c = √(a² + b²), the rule behind the 3-4-5 triangle.
• Q
• Quadratic FormulaSolve ax² + bx + c = 0 for both roots and see the discriminant that decides how many real solutions there are.
• Quarter Circle Area CalculatorThe area of a quarter circle from its radius — a quarter of πr², with the arc and the full perimeter alongside.
• R
• Radioactive Decay CalculatorHow much of a radioactive sample is left after a given time — from the starting amount and the half-life.
• Ratio CalculatorSolve A : B = C : D for the missing fourth term, with the reference ratio reduced to its lowest whole numbers.
• RC High-Pass Filter CalculatorCutoff frequency of a first-order RC high-pass filter from resistance in ohms and capacitance in microfarads — f_c = 1 / (2π × R × C).
• RC Low-Pass Filter CalculatorCutoff frequency of a first-order RC low-pass filter from resistance in ohms and capacitance in microfarads — f_c = 1 / (2π × R × C).
• RC Time Constant CalculatorThe time constant of an RC circuit, τ = R × C, in seconds from resistance in ohms and capacitance in farads.
• Reading Time CalculatorHow long a text takes to read: the word count divided by a reading speed in words per minute.
• Rebar Weight CalculatorWeight of a run of reinforcing bar from its designation and total length, in kilograms or pounds.
• Rectangle Area CalculatorThe area of a rectangle from its length and width, with the perimeter and the diagonal alongside.
• Rectangular Prism Volume CalculatorThe volume of a box from its length, width and height — simply the three multiplied.
• Redshift CalculatorRedshift z of a spectral line from its observed and rest wavelength — the fractional stretch of the light.
• Refractive Index CalculatorRefractive index of a medium from the speed of light inside it, against the exact vacuum value of 299792458 m/s.
• Regular Dodecahedron Volume CalculatorVolume of a regular dodecahedron from one edge length, with the surface area of every example beside it.
• Regular Icosahedron Volume CalculatorVolume of a regular icosahedron from one edge length, with the surface area of every example beside it.
• Regular Octahedron Volume CalculatorVolume of a regular octahedron from one edge length, with the surface area of every example beside it.
• Regular Polygon Area CalculatorThe area of a regular polygon from the number of sides and the length of one side.
• Regular Tetrahedron Volume CalculatorVolume of a regular tetrahedron from one edge length, with its surface area and height beside it.
• Resultant Force CalculatorThe single force that replaces two forces acting at an angle — magnitude from the parallelogram of forces.
• Reverberation Time CalculatorSabine reverberation time RT60 from room volume, total surface area and the average absorption coefficient.
• Reverse Percentage CalculatorFind the original value before a percentage increase or discount, or the whole from a known share. Choose a mode and see the formula and examples.
• Reynolds Number CalculatorReynolds number from density, velocity, characteristic length and dynamic viscosity — laminar or turbulent.
• Rhombus Area CalculatorThe area of a rhombus from its two diagonals — half their product, d₁ × d₂ ÷ 2, with the halving that is easy to forget.
• Right Triangle CalculatorArea, hypotenuse, perimeter and both acute angles of a right triangle from its two legs — area = ½ × a × b.
• Ring Size ConverterInner diameter in millimetres converted to a US ring size, with the EU/ISO circumference alongside.
• RL Time Constant CalculatorThe time constant of a resistor–inductor circuit, τ = L / R, in milliseconds from inductance and resistance.
• RMS Voltage CalculatorThe RMS voltage of a sine wave from its peak voltage — the effective value, peak divided by √2.
• Road Grade CalculatorThe grade of a road or path as a percentage, from the vertical rise and the horizontal run — with the matching angle.
• Rocket Equation CalculatorDelta-v of a rocket from its exhaust velocity and its wet and dry mass, using the Tsiolkovsky rocket equation.
• Roman Numeral ConverterTurn any whole number from 1 to 3999 into its standard Roman numeral, with the subtractive forms IV, IX, XL, XC, CD and CM.
• Rydberg Equation CalculatorWavelength of a hydrogen spectral line in nanometres from the two principal quantum numbers of the transition.
• S
• Scale CalculatorTurns a length measured on a model or map into the real-world length for any 1:N scale.
• Schwarzschild Radius CalculatorEvent-horizon radius of a mass, r = 2GM/c², in metres — the size it would have as a non-rotating black hole.
• Scientific Notation ConverterConvert any decimal number into scientific notation — a coefficient between 1 and 10 times a power of ten, with the exponent shown.
• Screen Width CalculatorPhysical width of a screen from its diagonal and aspect ratio, with the matching height in the table below.
• Sector Area CalculatorThe area of a circular sector — a pie slice — from the radius and its angle in degrees.
• Semicircle Area CalculatorThe area of a half circle from its radius — half of π times the radius squared.
• Series Capacitance CalculatorThe combined capacitance of two capacitors in series, by the product-over-sum rule C = C1C2 ÷ (C1 + C2).
• Series Resistor CalculatorThe total resistance of two resistors in series, where the values simply add: R = R1 + R2.
• Shoe Size ConverterConvert between EU, UK, US men's and women's shoe sizes and foot length in cm.
• Significant Figures CalculatorRound any number to a given number of significant figures, leading zeros excluded.
• Skin Depth CalculatorHow deep an alternating current runs in a conductor, from the frequency, the resistivity and the relative permeability.
• Slope CalculatorThe slope of the straight line through two points — the change in y divided by the change in x, or rise over run.
• Snell's Law CalculatorAngle of refraction in degrees from the two refractive indices and the angle of incidence, measured from the normal.
• Solar Panel Output CalculatorThe daily energy of a solar panel or array in kWh, from its wattage, the peak sun hours and a performance ratio.
• Solution Dilution CalculatorHow much stock solution to measure out: V₁ = C₂ × V₂ ÷ C₁. The solvent you top up with is the final volume minus that.
• Sound Intensity Level CalculatorSound intensity level in decibels from a measured intensity in W/m², against the 1e-12 W/m² threshold of hearing.
• Sound Level at Distance CalculatorHow far a noise level drops with distance in a free field: doubling the distance from a point source costs about 6 dB.
• Specific Gravity CalculatorRelative density of a substance against water — a dimensionless ratio that tells you at a glance whether it sinks or floats.
• Specific Heat Capacity CalculatorThe specific heat capacity of a material in J/(kg·K), from the heat added, the mass heated and the temperature rise.
• Specific Impulse CalculatorThe specific impulse of a rocket engine in seconds, from its thrust in newtons and its propellant mass flow in kg/s.
• Specific Weight CalculatorWeight density of a material — γ = ρ × g, in newtons per cubic metre, for any local gravity.
• Speed ConverterConvert km/h, mph, metres per second, feet per second and knots with exact factors, in either direction.
• Speed of Sound CalculatorThe speed of sound in dry air for any air temperature, using v = 331.3 + 0.606 × T.
• Speed, Distance and Time CalculatorAverage speed in km/h from a distance in kilometres and a time in hours — plus the pace behind it.
• Sphere Surface Area CalculatorThe surface area of a sphere from its radius — four π times the radius squared.
• Sphere Volume CalculatorThe volume of a sphere from its radius — four thirds of π times the radius cubed.
• Spherical Cap Surface Area CalculatorThe surface area of a dome cut from a sphere — the curved skin, 2πRh — from radius and cap height.
• Spherical Cap Volume CalculatorThe volume of the dome cut off a sphere, from the sphere radius and the height of the cap.
• Spherical Sector Volume CalculatorThe volume of the ice-cream-cone solid from a sphere's centre out to a cap: V = 2πR²h/3.
• Spherical Segment Volume CalculatorThe volume of a spherical segment — the slice of a sphere between two parallel planes — from both base radii and the height.
• Spherical Wedge Volume CalculatorThe volume of a spherical wedge — one orange slice of a sphere — from the sphere radius and the wedge angle in degrees.
• Spring Mass Period CalculatorThe period of a mass on a spring from the mass and the spring constant — one full oscillation in seconds.
• Spring Potential Energy CalculatorThe elastic energy stored in a stretched or compressed spring, E = ½ × k × x², in joules from its spring constant and displacement.
• Square Footage CalculatorCalculate one rectangle, identical areas or up to 20 different rectangular rooms. Enter feet and inches or metres; read ft², yd² and m².
• Stefan-Boltzmann Law CalculatorRadiated power of an ideal blackbody in watts from its surface area and its absolute temperature in kelvin.
• Stopping Distance CalculatorTotal stopping distance of a vehicle — reaction distance plus braking distance, from speed, grip and reaction time.
• Surface Gravity CalculatorSurface gravity of a planet or moon from its mass and radius, g = GM/r², in metres per second squared.
• Surface Speed CalculatorCutting or rim speed of a rotating part — v = π × d × n, with the diameter in metres and the speed in rpm.
• T
• Tangential Velocity CalculatorLinear speed of a point on a rotating body in m/s, from the angular velocity in rad/s and the distance to the axis.
• Tank Volume CalculatorCapacity of a cylindrical, rectangular or capsule tank in litres, from the dimensions your chosen shape actually needs.
• Temperature ConverterConvert temperature between Celsius, Fahrenheit and Kelvin, with the zero-point offset handled properly.
• Terminal Velocity CalculatorSteady fall speed from mass, frontal area, drag coefficient and fluid density — the point where drag balances weight.
• Test Grade CalculatorYour test score as a percentage from the points you earned and the total available, with the US letter bands.
• Thermal Expansion CalculatorHow much a solid grows or shrinks with temperature: ΔL = α × L₀ × ΔT, from the expansion coefficient, length and temperature change.
• Thermal Resistance CalculatorThe absolute thermal resistance of a flat layer in K/W, from its thickness, thermal conductivity and area.
• Thin Lens Equation CalculatorImage distance from focal length and object distance — the sign tells you whether the image is real or virtual.
• Three-Phase Power CalculatorReal power of a balanced three-phase load from line-to-line voltage, line current and power factor.
• Thrust-to-Weight Ratio CalculatorThe thrust-to-weight ratio of a rocket, drone or jet from its thrust in newtons and its total mass in kilograms.
• Torque CalculatorTorque in newton-metres from a force and the length of the lever arm it pulls on, with the force at a right angle to the arm.
• Torque ConverterConvert torque between newton-metre, kilonewton-metre, pound-foot, pound-inch, kilogram-force metre and ounce-force inch.
• Torque to Horsepower CalculatorEngine power in mechanical horsepower from torque in pound-feet and engine speed in rpm, using the 5252 constant.
• Torricelli Velocity CalculatorEfflux speed of fluid leaving an opening below the surface — Torricelli's law, v = √(2gh).
• Torus Surface Area CalculatorThe surface area of a torus from its major and minor radius: 4π²Rr, the tube's circumference carried once round the ring.
• Torus Volume CalculatorThe volume of a torus — a doughnut or ring — from its major and minor radius.
• Transformer Turns Ratio CalculatorSecondary voltage of an ideal transformer from the primary voltage and both turns counts.
• Trapezoid Area CalculatorThe area of a trapezoid (UK: trapezium) from its two parallel sides and the perpendicular height.
• Triangle Area CalculatorThe area of a triangle from one base and the perpendicular height measured to that base.
• Triangle Area from CoordinatesThe area of a triangle from the coordinates of its three vertices, by the shoelace formula.
• Triangular Prism Surface Area CalculatorThe surface area of a triangular prism from its three triangle sides and its length, via Heron's formula.
• Triangular Prism Volume CalculatorThe volume of a triangular prism from the triangle's base and height and the prism's length.
• U
• Unit Price CalculatorPrice per unit and per 100 units from a pack price and its quantity — the figure that compares pack sizes.
• V
• Vector Magnitude CalculatorThe length of a 3D vector from its x, y and z components — the Pythagorean theorem with one more axis.
• Voltage Divider CalculatorOutput voltage of a two-resistor divider from the input voltage, R₁ and R₂.
• Voltage Drop CalculatorEstimate DC, single-phase or three-phase wire voltage drop from current, one-way length and conductor; see V, %, and load voltage.
• Volume ConverterConvert litres, cubic metres, cups, fluid ounces, pints, quarts and both gallons with exact factors, in either direction.
• Volumetric Flow Rate CalculatorVolumetric flow rate in cubic metres per second from the cross-sectional area and the flow velocity.
• W
• Watts to Amps CalculatorCurrent in amps from power in watts and supply voltage, using I = P ÷ V.
• Watts to Lumens CalculatorBrightness in lumens from a lamp's power in watts and its luminous efficacy in lumens per watt.
• Wavelength CalculatorWavelength of an electromagnetic wave from its frequency, using the exact vacuum speed of light 299792458 m/s.
• Weight ConverterConvert grams, kilograms, metric tonnes, ounces, pounds and stone with exact factors, in either direction.
• Weight Force CalculatorThe weight of a mass in newtons — mass times the local gravitational acceleration, on Earth, the Moon or Mars.
• Weight on Other Planets CalculatorWhat you would weigh on the Moon, Mars, Jupiter or the Sun — your Earth weight scaled by each body's gravity.
• Weighted Average CalculatorCalculate the weighted average of two scores, grades or values. Enter each weight and see the formula and worked examples; weights need not total 100.
• Weighted Grade CalculatorYour weighted grade average from up to four grades and their weightings — written exams counting double, coursework counting once.
• Wh to mAh CalculatorBattery energy in watt-hours converted back to charge capacity in mAh using the nominal voltage.
• Wheatstone Bridge CalculatorThe unknown resistance of a balanced Wheatstone bridge from its three known resistors — Rx = R2 × R3 ÷ R1.
• Wien's Displacement Law CalculatorPeak emission wavelength of a blackbody in nanometres from its absolute temperature — the Wien constant over T.
• Wind Chill CalculatorThe wind chill in °C from the air temperature and the wind speed, using the metric North American formula.
• Wind Turbine Power CalculatorThe mechanical power at a wind turbine rotor in watts, from air density, swept area, wind speed and power coefficient.
• Wire Resistance CalculatorThe resistance of a conductor from its resistivity, length and cross-sectional area — R = ρ × L / A, in ohms.
• Words Per Page CalculatorHow many pages a word count fills at 11 or 12 point, single or double spaced — the standard typesetting figures.
• Work CalculatorMechanical work in joules from a constant force, the distance moved, and the angle between them.
• Y
• Young's Modulus CalculatorStiffness of a material from the pulling force, the cross-section and how far it stretches — E = stress ÷ strain, in pascals.