One Rep Max Calculator

The One Rep Max Calculator estimates the most weight you could lift for a single rep (1RM) from a set you’ve done, using the Epley and Brzycki formulas. It also gives a percentage table of working weights for different rep targets. Epley and Brzycki tend to agree closely within the 1–10 rep range this calculator is built for, but they diverge more as reps climb — Brzycki's formula also breaks down mathematically as reps approach 37 (its denominator, 37 − reps, approaches zero), which is one reason this calculator caps input at 20 reps rather than letting it run higher. Both formulas were validated primarily on major compound barbell lifts like the bench press, back squat, and deadlift, and tend to be less reliable for lifts with a heavier stabilization or skill component — think overhead presses or Olympic lifts — where technique breakdown can limit reps before muscular fatigue does. Because the estimate is a projection from a submaximal set rather than a directly tested max, factors like sleep, hydration, and how close to true failure the set was taken can shift the real number by several percent in either direction.