Brzycki 1rm
Calculator

It calculates one-rep max as weight × 36 / (37 − reps), based on an assumed linear decline in strength as reps increase. Enter the weight you lifted and how many reps you completed to get an estimated single-rep maximum.

The formula assumes a roughly linear relationship between reps and load that breaks down as sets get longer and muscular endurance starts playing a bigger role than pure strength. Estimates from sets of 10+ reps tend to overestimate true 1RM compared to lower-rep tests.

Both estimate 1RM from submaximal reps but use different mathematical models; they typically agree closely in the 1-5 rep range and diverge more as reps increase, with Brzycki often producing slightly more conservative estimates at higher rep counts. Neither is definitively more accurate for every lifter.

It works reasonably well for major compound lifts like squat, bench, and deadlift, where the tested rep range was originally derived, but accuracy can be less reliable for isolation or bodyweight exercises with different fatigue patterns. Treat estimates for non-barbell movements as rougher approximations.

If you complete more reps with the same weight than you did previously, the formula projects a higher 1RM, reflecting a genuine strength or endurance improvement. This makes the formula useful for tracking progress even without regularly testing an actual 1RM.