One Rep Max (1RM) Calculator

How the One Rep Max Calculator Works

This calculator estimates your one-repetition maximum (1RM) — the heaviest weight you could lift once with proper form — using four established formulas. Instead of risking injury by attempting an actual maximal lift, you can input a weight you have successfully lifted for multiple repetitions and get a reliable 1RM estimate.

The four formulas included are: Epley (w × (1 + r/30)), Brzycki (w × 36/(37 - r)), Lander (100 × w / (101.3 - 2.67123 × r)), and Lombardi (w × r^0.1). Each approaches the estimation differently, and the average of all four provides a balanced estimate. These formulas are most accurate for rep ranges between 1 and 10.

Below the 1RM estimates, the percentage table shows training loads from 50% to 100% of your estimated 1RM in 5% increments. This is invaluable for programming your workouts: use 90-100% for pure strength work (1-3 reps), 75-85% for strength and muscle building (5-8 reps), and 60-75% for hypertrophy and endurance (8-15 reps). Whether you are following a percentage-based program like 5/3/1, Starting Strength, or designing your own routine, this tool eliminates the guesswork from load selection.