Epley Formula Calculator for 1RM

The Epley formula estimates a one rep max as weight × (1 + reps ÷ 30): each rep you complete adds one thirtieth of the bar weight to the estimate. It is the equation most gym apps run by default. Enter your set below — the calculator shows Epley and, for contrast, Brzycki.

Worked example

Take 220 lb (100 kg) for 6 reps:

100 × (1 + 6 ÷ 30) = 100 × 1.20 = 120 kg, or about 265 lb.

The structure is worth noticing. The bonus per rep is constant, so the line never bends: at 20 reps Epley would credit you with a max of 167 kg from that same 100 kg, and at 40 reps it would say 233 kg. Nothing stops it. Brzycki, by contrast, has a built-in ceiling near 37 reps, and the two agree exactly at 10 reps. That crossing point is the reason Epley reads low under 10 reps and high above them, relative to its rival.

Where the equation came from

Not from a laboratory. Epley’s formula was extracted from a poundage chart published in a resistance training manual for athletes at the University of Nebraska in 1985; there is no documented sample, protocol or error term behind it. Brzycki’s 1993 equation has the same pedigree — a practitioner article aimed at coaches, offered as a working tool. Both spread because they were useful and easy to compute, not because they beat a rival in a trial.

That history explains a modern finding. When a 2026 preprint fitted the same functional form to 303,494 near-failure sets across 388 exercises, the four classic equations came out nearly indistinguishable from each other — Epley, Brzycki and Wathen sat within a rounding error on the same consistency metric — and all four were beaten by about 17% once the divisor was allowed to depend on the weight lifted. Their shared weakness is the fixed 30, not the arithmetic around it.

When to trust it

Keep the reference set at 10 reps or fewer, taken with clean technique and stopped a rep or two short of failure. Mayhew’s comparison of published equations against measured maxes found accuracy improved once the set stayed inside that range, which is also the range every classic formula was drawn from. Long sets are governed by fatigue resistance as much as by strength, and that is not what the divisor 30 encodes.

For the head-to-head against the other classic model, see the Brzycki formula calculator and the full comparison on Epley vs Brzycki. To average both equations on one screen, use the one rep max calculator; to convert the result into training loads, the 1RM percentage chart.