Enter the weight you just lifted and the reps you completed with it, and the page returns an estimated one-rep max along with the share of that max the weight represents. It runs both the widely used Epley and Brzycki formulas side by side and shows the gap, so you never work from a converted number without knowing which formula produced it. It is a reverse calculator for managing intensity without testing a true one-rep max.
The formulas applied are Epley, one-rep max equals weight times one plus reps divided by thirty, and Brzycki, weight times thirty-six divided by thirty-seven minus reps. Percent of max divides your entered weight by each formula result, and the table applies the same formulas in reverse for target rep counts. At one rep the weight is your max by definition, so both columns keep your input, and the result notes that Epley would run 3.33% higher. Brzycki divides by zero at thirty-seven reps, which is why input stops at thirty. As of October 2026 both remain published estimates rather than measurements.
This page prescribes no rep range, set count or rest period for any goal. Past ten reps the two formulas separate quickly, so do not take a converted figure straight to the bar as a training weight. Test a true max only with a spotter, and stop rather than convert if a movement is painful.
Frequently Asked Questions
Neither can be called more accurate across the board. Both are estimates, so this page shows both results and the gap and leaves the choice to you.
A weight lifted once is the one-rep max by definition. Epley would return a figure 3.33% higher, so the formula is not applied in that case.
Brzycki divides by zero at thirty-seven reps and climbs steeply near it. Past ten reps the two formulas already diverge noticeably.