Case 1
- Moles of solute (mol)
- 0.5mol
- Volume of solution (L)
- 2L
0.2500mol/L
Open with these valuesMolarity Calculator
0.2500mol/L
Result: 0.2500 mol/LMolarity is moles of solute divided by litres of solution: 0.5 mol in 2 L gives 0.25 mol/L, also written 0.25 M. Use the volume of the finished solution, not the solvent you started with. Litres, never millilitres — 250 mL is 0.25 L, and mixing the two is a factor of a thousand.
Worked examples
Case 2
- Moles of solute (mol)
- 1mol
- Volume of solution (L)
- 1L
1.0000mol/L
Open with these valuesCase 3
- Moles of solute (mol)
- 0.1mol
- Volume of solution (L)
- 0.25L
0.4000mol/L
Open with these valuesHow it's calculated
Molarity = moles ÷ litres of solution
- StepEnter the amount of solute in moles.
- StepEnter the volume of the finished solution in litres — 250 mL is 0.25 L.
- ResultRead the concentration in mol/L; 1 mol/L is written 1 M.
What this number means
Per litre of solution, not of solvent
Molarity is defined per litre of the finished solution. Dissolve the solute and then top up to the wanted volume in a volumetric flask — that is the standard lab method.
Litres, never millilitres
The volume field is in litres, so 250 mL goes in as 0.25 L. With 0.1 mol that gives 0.4 mol/L; mixing the two units is a factor of a thousand.
1 mol/L is written 1 M
A 1 M solution holds one mole of solute per litre of solution. Below 1 M is dilute, above it concentrated; household vinegar is roughly 0.8 M acetic acid.
Molarity moves a little with temperature
It depends on the volume of the solution, and liquids expand when heated. The same amount of solute over a larger volume gives a marginally lower molarity.
Commonly misread
I dissolved 0.5 mol in 2 L of water, so the solution is 0.25 mol/L.
Only if the finished solution measures 2 L. Molarity counts litres of solution, not litres of solvent you started with.
0.1 mol in 250 mL is 0.1 ÷ 250.
The field takes litres: 250 mL is 0.25 L, so it is 0.1 ÷ 0.25 = 0.4 mol/L.
Zero moles is not a valid entry.
It is allowed and returns 0 mol/L, pure solvent. Only the volume has to stay above zero.
Reference table
| Moles (mol), volume (L) | Description | Molarity (mol/L) |
|---|---|---|
| 0, 1 | Pure solvent | 0 |
| 0.1, 0.25 | Small flask | 0.4 |
| 0.5, 2 | Dilute solution | 0.25 |
| 1, 1 | One molar | 1 |
| 2, 0.5 | Concentrated solution | 4 |
Questions
How do I calculate molarity?
Divide the moles of solute by the volume of solution in litres: molarity = moles ÷ volume. For 0.5 mol of solute dissolved in 2 L of solution, that is 0.5 ÷ 2 = 0.25 mol/L. Keep the amount in moles and the volume in litres to get the result in mol/L.
What units does the molarity calculator use?
Solute amount in moles (mol), solution volume in litres (L), and molarity in moles per litre (mol/L). The unit mol/L is also written M and read as molar, so 0.25 mol/L is the same as 0.25 M.
Do I use the volume of solution or of solvent?
Always the total volume of the finished solution, not the volume of solvent you started with. Molarity is defined per litre of solution, so dissolving solute and then topping up to a known volume in a volumetric flask is the standard lab method.
What does 1 M (one molar) mean?
A 1 M solution contains one mole of solute per litre of solution. Concentrations below 1 M are dilute and those above 1 M are concentrated. For comparison, household vinegar is roughly 0.8 M acetic acid.
Does molarity change with temperature?
Slightly, yes. Molarity depends on the volume of the solution, and liquids expand when heated, so the same amount of solute spread over a larger volume gives a marginally lower molarity. For precise work, prepare and use solutions at a stated temperature.
Sources and last check
Information, not professional advice.