Case 1
- Weight lifted
- 100kg
- Repetitions
- 5
- Equation
- Epley
116.7kg
Open with these valuesOne Rep Max Calculator
116.7kg
Result: 116.7 kgYour one-rep max is the heaviest load you could lift once. It can be estimated from a lighter set taken close to failure — the fewer the repetitions, the closer the estimate.
The numbers at a glance
Held fixed: Weight lifted 100.0 kg, Equation Epley.
| Repetitions | Result (kg) |
|---|---|
| 2 | 106.7 |
| 4 | 113.3 |
| 5Your value | 116.7 |
| 6 | 120.0 |
| 8 | 126.7 |
Worked examples
Case 2
- Weight lifted
- 140kg
- Repetitions
- 3
- Equation
- Brzycki
148.2kg
Open with these valuesCase 3
- Weight lifted
- 60kg
- Repetitions
- 8
- Equation
- O’Conner
72.0kg
Open with these valuesHow it's calculated
Epley: 1RM = kg × (1 + n/30)
- StepEnter the load you lifted and how many clean repetitions you managed.
- StepPick an equation — Epley is the common default.
- StepRead the estimated one-rep max.
- ResultCompare a second equation to see how wide the estimate really is.
What this number means
A one-rep max is the heaviest load you could lift once, and this page estimates it from a set you have already done. Each of the five equations takes that set — a load and a repetition count — and extrapolates along a fitted curve back to a single repetition. Epley, the default, adds a thirtieth of the load for every repetition: 100 kg for five repetitions is 100 × (1 + 5/30), or 116.7 kg. The same set returns 112.5 kg through Brzycki, 112.5 through O’Conner, 113.7 through Lander and 117.5 through Lombardi. Read the result as a band rather than a point. Five kilos separate the highest and the lowest estimate for one identical set, and that spread is the resolution of the method, not a fault in any single equation. It is also why a change of equation is not a change in strength. The estimate rests entirely on the set having been taken close to failure, because a repetition held back is, to the formula, indistinguishable from one that was not there: entering a set with two in reserve as if it were maximal lifts the result by roughly what two further repetitions would add. It holds up best from sets of five or fewer; at ten repetitions the same 100 kg reads 133.3 kg by Epley. What comes out is an estimate from a fitted curve, not a lift that has happened.
Run the set through a second equation
The five equations agree closely at low repetitions and drift apart as the set gets longer. The spread between two of them is the honest width of the estimate.
It assumes the set was close to failure
Leaving two repetitions in reserve and entering the set as if it were maximal moves the result up by roughly the same amount two more repetitions would.
Best from sets of five or fewer
The estimate degrades as the set gets longer. At ten repetitions the same 100 kg gives 133.3 kg by Epley, and errors of that size are why short sets are the usual basis.
Commonly misread
The calculator says 116.7 kg, so that is my one-rep max.
It is an estimate from a fitted curve, not a measurement. On the same set the other equations here return as little as 112.5 kg.
Epley returns 103.3 kg for a single 100 kg lift, so the calculator is wrong.
Some of the equations are fitted curves that do not pass exactly through the single-repetition point. Brzycki and Lombardi return the 100 kg you entered.
I estimated from a set of ten, so the number is just as good.
Accuracy falls away with longer sets. Ten repetitions at 100 kg give 133.3 kg by Epley, which is why estimates are usually taken from five or fewer.
Questions
What is a one-rep max?
The heaviest load you could lift once. It can be estimated from a lighter set taken close to failure, and the fewer the repetitions the closer the estimate.
Which equation should I use?
They agree closely at low repetitions and drift apart as the set gets longer. At 100 kg for five repetitions the five here give 112.5, 112.5, 113.7, 116.7 and 117.5 kg.
How accurate is the estimate?
It rests on the set having been taken close to failure. Leaving two repetitions in reserve and entering the set as if it were maximal moves the result up by roughly the same amount two more repetitions would.
Why does the result exceed the weight at one repetition?
Because some of the equations are fitted curves that do not pass exactly through the single-repetition point. At 100 kg for one repetition Epley returns 103.3 kg while Brzycki and Lombardi return the 100 kg you entered.
Does the estimate hold for long sets?
It degrades. At ten repetitions the same 100 kg gives 133.3 kg by Epley, and errors of that size are why estimates are usually taken from sets of five or fewer.
Sources and last check
Information, not medical advice.