One Rep Max (1RM) Calculator

Testing a true one-rep max is tiring and carries injury risk, especially without a spotter. This calculator estimates it from a set you've already done — enter the weight and the number of reps, and get your predicted 1RM.

How the Epley formula works

The calculator uses Epley: 1RM = weight × (1 + reps ÷ 30). For example, 100 kg for 5 reps gives 100 × (1 + 5/30) ≈ 116.7 kg. The formula works with any unit, so pounds in means pounds out.

How accurate is it?

Estimates are most reliable from sets of about 2 to 10 reps. Above that, fatigue and conditioning affect the result more than strength does, so predictions drift. Different formulas also disagree slightly — Brzycki, for example, predicts about 112.5 kg for the same 100 kg × 5 set. Treat the number as a guide, not a guarantee.

Using your 1RM in training

Many programs prescribe work as a percentage of 1RM — for example, sets at 70–85% for building strength and size. Recalculating every few weeks from a recent hard set keeps those percentages up to date without max testing.