Evidence-aware · beginner-first · no miracle claims
The one-rep max calculator: what your reps say about your strength
In one line: Enter a weight and how many times you lifted it - get an estimated one-rep max and a full training-weight table. Nothing leaves your browser.
Every strength plan speaks one language: percentages of your one-rep max, or 1RM - the most weight you could lift for a single, honest rep. Testing it for real is risky and exhausting. Estimating it from a normal set takes ten seconds and is accurate enough to programme with.
The calculator
How to read the table
The estimate arrives with a table of training weights. The usual map: sets of 3-6 reps around 85-93% build maximal strength, sets of 6-12 around 67-85% build muscle size almost as well, and anything lighter builds endurance. You do not need to be precious about it - two or three percent either way changes nothing.
The honest caveats. The estimate uses the Epley formula, one of several respectable formulas: 1RM = weight x (1 + reps/30). It is an estimate, not a measurement, and it drifts above 10 reps - which is why the input stops at 12. Rounding to the nearest 2.5 kg is deliberate: barbells move in 2.5 kg jumps anyway.
Do you need to test a true max? Almost never, and not as a beginner. Training at 75-85% for 3-8 reps builds the same strength with a fraction of the injury risk. If you ever do test, it is with a spotter, after weeks of practice on the lift - not on a dare.
Numbers here are approximate and for healthy adults building general strength - not medical advice, and results are not guaranteed. Pair the table with the exercise library; the workout builder turns it into a week. More arithmetic lives on the fitness calculators page.
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General information, not medical advice. If you have a health condition, have been inactive for a long time, or something hurts sharply, talk to a qualified health professional first.