One-Rep Max (Epley) Calculator

About this calculator

The Epley formula, published by Boyd Epley in 1985, estimates a lifter's true one-rep max from a lighter set taken close to failure: 1RM = weight × (1 + reps ÷ 30). It's built on the observation that strength and endurance trade off in a roughly linear way at moderate rep ranges — lifting a weight for 10 reps implies a 1RM about a third heavier than that weight.

Strength coaches use it so athletes don't have to attempt a genuine, injury-risking single-rep max just to program percentages for the week's training. It's most accurate in the 2–10 rep range; because the formula is linear, it tends to overestimate 1RM once the rep count climbs much higher.