One Rep Max Calculator

A one-rep max (1RM) is the maximum amount of weight you can lift for a given exercise for exactly one complete repetition with proper form. It is the standard measure of maximal strength in resistance training and is used to prescribe training loads · workouts are often programmed as a percentage of 1RM (e.g., 3 sets of 5 reps at 80% 1RM).

Several validated formulas estimate 1RM from submaximal lifts. The most widely used is the Epley formula: 1RM = weight × (1 + reps/30). The Brzycki formula is: 1RM = weight × 36 / (37 − reps). These formulas are most accurate when using 3-10 rep sets; accuracy decreases significantly above 10 reps. For example, if you lift 100 kg for 5 reps using the Epley formula: 1RM ≈ 100 × (1 + 5/30) ≈ 117 kg.

For most recreational lifters, formally testing 1RM every 8-16 weeks is sufficient · this aligns with typical training block lengths. Frequent maximal testing is taxing on the central nervous system and joints and offers limited benefit unless you compete in powerlifting or Olympic lifting. Many intermediate and advanced athletes prefer to estimate 1RM from submaximal lifts (e.g., a heavy 3-5 rep set) rather than true single-rep maximal attempts.