One Rep Max Calculator

How your one-rep max is estimated

Your one-rep max (1RM) is the most weight you can lift for a single rep, but you do not have to actually attempt a max to know it. From a set you can already do, two established formulas estimate it: Epley (weight × [1 + reps ÷ 30]) and Brzycki (weight × 36 ÷ [37 − reps]). This tool runs both and shows their average as your headline number, plus each formula on its own so you can see the range. Lift 100 kg for 5 reps, for instance, and your estimated max is about 115 kg.

Why it is most accurate for low reps

Rep-max formulas were built around heavy sets, so they are most trustworthy from 1 to about 10 reps. The further past that you go, the more your result depends on conditioning and pacing rather than raw strength, and the estimate drifts high — which is why the calculator flags higher-rep sets as less reliable. For the sharpest number, use a hard set of 3 to 8 clean reps rather than a light set taken to failure.

Using the percentage chart to program

Most strength routines prescribe load as a percentage of your 1RM — a 5×5 at 80%, a heavy single at 95%, back-off sets at 70%. The chart takes your estimated max and lays out the weight at each common percentage next to the reps you would expect to manage there, so you can pick a working weight in seconds. Pair heavy training with enough fuel and recovery: the Protein Calculator sets your daily protein to build and keep muscle, and the TDEE Calculator shows the calories to support it.