Epley One-Repetition Maximum Estimate

A one-repetition maximum (1RM) is the greatest load a person can lift once for a specified exercise using acceptable technique. This calculator estimates 1RM from a submaximal set. It can help describe a completed training set, but it does not test technique, fatigue, pain, equipment setup, or readiness to attempt a heavy lift.

Method and formula

For sets of two or more repetitions, the tool implements the Epley equation:

1RM = weight × (1 + repetitions ÷ 30)

For one completed repetition, the estimate is the entered weight itself. This special case avoids making a known single lift 3.33% heavier through extrapolation.

The input accepts 1 to 12 repetitions and a positive weight. The result table estimates loads for one through ten repetitions by algebraically rearranging the same equation. It does not mix percentages or formulas from a different model.

Worked example

Suppose a lifter completes 50 kg for 10 repetitions:

50 × (1 + 10 ÷ 30) = 66.67 kg

The number is a model estimate, not proof that the lifter can safely complete 66.67 kg once. Exercise selection, range of motion, repetition speed, rest, and measurement accuracy can all change the relationship between a repetition set and a true maximum.

How to interpret the result

Use the estimate as a consistent tracking reference for the same exercise and similar conditions. For example, comparing estimates from two well-documented bench-press sets may show a trend without requiring frequent maximal testing.

Do not compare estimates across unlike movements as though they measured one universal strength score. A squat estimate and a shoulder-press estimate reflect different movement patterns and muscle groups.

Limits and training safety

• Prediction error grows as a set moves farther from a single repetition. Published validation work cautions that linear 1RM equations should generally use no more than ten repetitions; this interface permits up to 12 for compatibility but results above ten deserve extra caution.
• The equation assumes the entered set was performed through a consistent range of motion and ended near the lifter's current repetition limit. Stopping early can understate capacity; degraded technique can make the input unsuitable.
• The estimate does not prescribe a load, training plan, or safe attempt. Heavy lifting can cause injury. Use appropriate equipment, progressive loading, competent supervision or a spotter where relevant, and stop if pain or concerning symptoms occur.
• Medical conditions, pregnancy, recent surgery, injury, or unfamiliarity with resistance exercise may require individualized advice from a qualified health or exercise professional.

Sources

• LeSuer et al., The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift — comparison of prediction equations and repetition-count limitations.
• National Strength and Conditioning Association, NSCA's Guide to Tests and Assessments — professional context for selecting and administering strength assessments.

Editorial record

• Author: SoupCalc Editorial Team
• Method review: SoupCalc Fitness Content Review
• Last reviewed: August 10, 2026
• Review scope: implemented Epley equation, single-repetition handling, input limits, worked example, evidence, and safety language