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One-Rep Max (Epley) Calculator

Estimate your one-rep max with the Epley formula

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.

Worked example

You lift 80 kg for 6 reps. Step 1: reps ÷ 30 = 6 ÷ 30 = 0.2. Step 2: 1 + 0.2 = 1.2. Step 3: 80 × 1.2 = 96. The tool shows 96.00 kg as the estimated one-rep max. Doing 80 kg for just 1 rep would give 82.67 kg, since the formula adds a small amount even for one rep.

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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.

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.

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Comments (1)

  • Editorial team

    Programs are often written as percentages of a one-rep max, and this is where the estimate gets used. From the 96 kg example, 80 percent would be 76.8 kg. The output is labelled in kilograms, so enter kilograms for a correct label. Because it is only a prediction, test it with a heavier warm-up single before you build a plan on it. Which lift are you estimating, and how close to failure did the set end?

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