One Rep Max Calculator
A one rep max is the heaviest load you can lift once. Testing it directly is risky, so most lifters estimate it from a lighter set — and the whole topic is really about how much you should trust that estimate.
Estimated one rep max (Epley)
116.6667
- The same set under the Brzycki formula
- 112.5
- Load for a 90 per cent working set
- 105
- Reps a 75 per cent load typically supports
- 10
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
Epley: 1RM = w x (1 + reps/30) | Brzycki: 1RM = w x 36 / (37 - reps)
- w
- Weight lifted for the set you completed
- reps
- Repetitions completed with that weight
- 1RM
- Estimated one rep max, a prediction rather than a measurement
- share
- Working percentage of the one rep max, such as 0.9 or 0.75
How to check the result by hand
- 1
Complete a set with clean technique
Choose a weight you can lift for a known number of reps with good form, ideally five or fewer. The whole estimate rests on this set being a genuine effort rather than a comfortable warm-up, so it must be a set you actually finished. If in doubt, use a set on which you could have taken one or two more reps rather than one taken to absolute failure.
- 2
Record the weight and the reps exactly
For 100 kg for five reps, note both numbers precisely. A rounded weight or an uncertain rep count feeds straight into the estimate, and the formulas will happily produce a confident-looking answer from sloppy inputs.
- 3
Apply the Epley formula for the primary estimate
100 x (1 + 5/30) = 116.66667. This is the figure most programming tables assume, and it is the one the calculator reports first.
- 4
Apply the Brzycki formula as a cross-check
100 x 36 / (37 - 5) = 112.5. The two formulas differ by 4.1666667 kg on this set, which tells you the estimate carries a few kilograms of uncertainty and should not be treated as exact.
- 5
Convert the estimate into working loads
Take 90 per cent for a heavy set: 116.66667 x 0.9 = 105. A 75 per cent load typically supports around ten reps, so the single estimate becomes a set of training numbers rather than one figure. Written down, these figures cover a week of sessions without any further arithmetic.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate One Rep Max page.