One Rep Max Calculator

A one-rep max is the heaviest weight you can lift for a single clean repetition. It is the standard yardstick of strength and the anchor for percentage-based programmes, but testing it directly is risky, slow and needs a spotter. Estimation from a set you have already done is the practical alternative.

The four formulas here are the classics. Epley's is the simplest and most used: weight multiplied by one plus reps divided by thirty. Brzycki's uses a fraction that grows sharply as reps climb, so it predicts lower maxima for high-rep sets. Lombardi's raises the rep count to the power of 0.1, and Lander's is a rational function fitted to bench-press data. They agree closely at low reps and diverge as the set gets longer.

Accuracy falls off quickly above about ten reps, which is why the calculator caps there. At three to five reps the estimate is usually within a couple of percent of a tested max. At fifteen reps the same formula can be out by ten percent or more, because high-rep sets depend more on endurance than on raw strength, and because form breaks down differently from person to person. When you want a reliable number, test with three to five reps, not fifteen.

The percentage rows are what you will actually use day to day. Most strength programmes set working weights as a fraction of 1RM: around 70 percent for volume work, 80 percent for standard sets, 85 to 90 percent for heavy triples, and 90 percent plus for peaking. Re-estimate every few weeks; as you get stronger, the same set of five will move up, and the calculator will quietly tell you so. Do not chase a new one-rep max every session — building the estimate from submaximal work is safer and just as informative.

This calculator returns estimates for general information only. It is not medical advice, diagnosis or treatment, and it cannot replace an assessment by a qualified health professional. Individual results vary, and figures such as calorie needs, body-fat percentage and heart-rate zones are approximations based on population averages rather than measurements of you.