One Rep Max (1RM) Calculator

Your one rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form — the number every strength program is written around. Testing it for real is taxing and risky, so lifters estimate it instead: enter the weight you lifted and how many reps you got (2 to 12), and this calculator shows your estimated max instantly, in kilograms or pounds.

No single formula fits every lifter, so this tool computes four classic ones side by side: Epley (w·(1 + r/30)), Brzycki (w·36/(37 − r)), Lombardi (w·r^0.10) and O'Conner (w·(1 + r/40)), plus their average as a balanced headline number. Epley and Brzycki agree closely in the 2–10 rep range that most tests use; seeing all four at once shows you the realistic spread instead of one arbitrary answer.

Below the estimate you get a training percentage chart from 50% to 95% of your average 1RM in 5% steps — exactly the way programs prescribe working sets, whether it is 5×5 at 75%, hypertrophy work at 65–70% or heavy triples at 90%. Change the weight, reps or unit and everything recalculates live.

Everything runs locally in your browser as you type — no account, no app, and your training numbers never leave the page. Estimates from rep maxes are most accurate up to about 10 reps, so test with a moderately heavy set and let the formulas do the projecting.