Sports Performance

One-Rep Max Calculator

Estimate a single-repetition strength value from the weight and repetitions of a completed set.

Estimated one-rep max—

Percentages of estimate: —

How to use this calculator

  1. Enter the load actually lifted, choose kilograms or pounds, and enter the count of completed repetitions. Use a set for one specific exercise.
  2. Read the estimated one-rep max. A one-repetition input reports the observed load itself; for two or more repetitions the tool applies the Epley equation.
  3. Use the percentage rows as arithmetic reference values only. Choose training loads based on technique, fatigue, recovery, equipment, and competent coaching.

Epley one-rep max equation

For two or more completed repetitions, the Epley estimate is 1RM ≈ weight × (1 + repetitions/30). If you lifted 100 kg for five reps, the estimate is 100 × (1 + 5/30) ≈ 116.7 kg. This is an estimate based on a submaximal set, not a measured maximum.

When repetitions equal one, the load lifted is already an observed single for that set, so the calculator returns the entered weight rather than multiplying by 1 + 1/30. Whether it was truly the maximum possible lift still depends on effort and technique.

The formula is unit-preserving: input kilograms to receive kilograms, or pounds to receive pounds. A 100 lb set for five reps yields about 116.7 lb, not kilograms. It does not convert between lb and kg because the percentage calculation does not require conversion.

The tool accepts 1–20 whole repetitions but estimates generally become less dependable as repetition count rises. Research comparing equations shows their error varies by exercise and population. A 15-rep set should not be treated as a precise maximum test.

Using the estimate responsibly

For 80 kg lifted for six controlled reps, 1RM ≈ 80 × (1 + 6/30) = 96 kg. A displayed 80% reference load is 76.8 kg. The exact implement or available plates may require rounding down to a practical load.

A 90% row is not a command to attempt that load today. A previous set taken to failure, unfamiliar movement, injury, or poor spotting setup may change what is appropriate. Stop when form breaks down and follow qualified guidance for maximal testing.

Compare estimates only for the same exercise and similar range of motion and equipment. A barbell bench press value should not be interpreted as a dumbbell press or machine chest-press maximum. The formula describes the completed set, not whole-body strength.

Interpretation and limitations

Equation, not diagnosis

The result describes a simple empirical relationship between load and repetitions. It is not medical advice, a readiness score, or proof of a safe maximal weight.

High-repetition uncertainty

After about ten reps, fatigue tolerance increasingly affects the result. The tool flags higher-rep sets and avoids showing false precision beyond one decimal place.

Training percentages

The 60%–95% rows are just fractions of the estimate. They do not account for exercise-specific repetitions, velocity, warm-up, or recovery.

Test conditions

Technique, rest, spotting, training history, and range of motion matter. Use comparable test conditions if tracking changes over time.

Frequently asked questions

Why is my one-rep result the entered weight?

For one completed repetition, the entered load is the observed single. Applying a rep-prediction multiplier would incorrectly inflate that observation.

Can I use this for every lift?

The arithmetic works for a load and rep count, but predictive accuracy can differ substantially across lifts and individuals.

What if I entered pounds?

The answer and percentage loads remain in pounds. Select kg only when the input load is kilograms.

Should I test the displayed maximum?

No automatic recommendation follows from the estimate. A maximal attempt carries risk and should be planned with appropriate technique, equipment, supervision, and health considerations.

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Sources and review

Last reviewed: October 26, 2026. Calculations run in your browser. Verify original inputs before using results for training or reporting.

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