One-Rep Max (Epley) Calculator

How it is calculated

The Epley formula estimates the heaviest weight you could lift once from a lighter set done for several repetitions: 1RM = weight × (1 + reps ÷ 30). weight is the load you lifted (shown in kg), above zero, and reps is the number of clean repetitions you completed, at least 1. Each extra rep adds about 3.3% to the weight lifted. The result is an estimate: it assumes the set was taken to or near failure, and accuracy falls as the rep count rises, so sets of about 2 to 10 reps are most reliable. It cannot reflect your technique, fatigue or the exercise chosen. Other formulas give slightly different values.

Common mistakes

• Using a set with very many reps, such as 20 or 30. The estimate becomes unreliable because endurance, not strength, limits the set.
• Entering reps you stopped far short of failure. If you could have done 4 more, the formula underestimates your max.
• Testing the estimate with a true max attempt unprepared. The number is a guide for planning loads, not a safe target for a single heavy lift.
• Entering weight in pounds. The result is labelled kg, so the number must be in kilograms.
• Treating it as exact across exercises. Squat, bench and deadlift behave differently, so keep separate estimates.