One rep max calculator
Your one-rep max (1RM) is the most you can lift for a single rep, and you can estimate it without ever testing it. FitCalcs takes a set you can already do, a weight and the reps you got, and averages the Epley and Brzycki formulas. It then gives a percentage table so you can pick training loads: most strength work sits at 80 to 90 percent of your 1RM. The estimate is most accurate at ten reps or fewer. This is general information, and you should never test a true 1RM without a spotter and a proper warm-up.
How this is worked out
Your one-rep max (1RM) is estimated from a set you can already do, using two well-known formulas. FitCalcs shows the average of both:
Epley: 1RM = weight x (1 + reps ÷ 30)
Brzycki: 1RM = weight x 36 ÷ (37 − reps)
Both are most accurate at 10 reps or fewer; above that, estimates drift apart and read high. Use the percentage table to set training loads. The two formulas were published by Epley (1985) and Brzycki (1993).
Informational only. Never test a true 1RM without a spotter and a proper warm-up. Editorially reviewed by FitCalcs, with each figure citing its source.
Calculators and Data Desk, FitCalcs
FitCalcs' editorial desk builds and documents the calculators, citing the underlying equation and the UK dataset behind every number. Health-related tools are editorially reviewed, with figures cited to named UK sources.
Last reviewed: 12 June 2026