Estimate the maximum weight you could lift for a single repetition without actually attempting a risky one-rep max. Enter a weight you lifted and the number of clean reps you managed, and the calculator applies the well-known Epley and Brzycki formulas to predict your one rep max, showing both because they differ slightly and give a useful range. It then builds a percentage chart of that max, since most strength programs prescribe work as a percentage of your 1RM, so you can read off suggested loads for sets of different rep ranges. Estimates are most accurate for lower rep counts, roughly ten or fewer, and drift higher than reality beyond that. Use it to program safely and track progress. Everything is computed locally in your browser.