Estimate one-rep max with the Epley formula

This one-repetition maximum estimator converts a completed lifting set into an estimated maximum load for one repetition. Supply the weight lifted and the positive number of repetitions performed, and it applies the Epley equation: weight multiplied by one plus repetitions divided by thirty. The response preserves the weight unit you chose, so kilograms produce kilograms and pounds produce pounds. It is a planning estimate rather than a measured maximum, but it gives athletes, coaches, and training software a consistent reference without requiring a maximal attempt.

Enter a completed set that represents your current strength

Choose a set performed with controlled technique and enter the load as weight. Then enter repetitions as the positive whole number of successful repetitions completed at that load. Keep the same unit when comparing sessions or feeding results into another training system.

Weight must be a positive finite number, and repetitions must be a positive integer. Use repetitions you actually completed, not a planned target, and avoid counting assisted or partial repetitions unless that is the explicit convention of your program. A representative working set generally gives a more useful planning number than a set stopped far from fatigue, because the equation assumes the recorded performance says something meaningful about the lifter’s present capacity.

The calculator cannot judge technique, fatigue, range of motion, or whether the entered set was genuinely demanding, so data quality begins with the set you select.

Understand how the Epley estimate is calculated

For a weight of one hundred and five repetitions, the repetition adjustment is five divided by thirty, or one sixth, so the estimate is one hundred multiplied by seven sixths. The result is intentionally not rounded inside the algorithm; preserving the JavaScript numeric result avoids silently imposing a plate increment, display preference, or measurement precision that the caller did not request. A user interface may format the number for readability, while an automated consumer can apply its own rounding rule.

The estimate increases linearly with repetitions for a fixed weight, which is a property of the Epley equation rather than a claim that strength itself behaves linearly. Different maximum-strength formulas use different curves and may disagree, especially as repetition counts rise. This capability reports only Epley so the returned method is unambiguous.

Use the estimate for programming without treating it as a test result

An estimated one-repetition maximum is useful for selecting training percentages, comparing similar sets over time, and normalizing performance when the load and repetition count both change. A coach can estimate a reference maximum from a recent working set and calculate approximate loads for subsequent sessions without asking an athlete to perform a true maximal lift. The estimate is not a guarantee that the athlete can safely lift that load once.

Exercise skill, fatigue, equipment, tempo, range of motion, spotting, recent training, and individual repetition endurance can all move actual performance away from the equation. Compare like with like: use the same exercise variation, equipment setup, movement standard, and weight unit when tracking a trend. Very high repetition sets may be less representative of maximal strength because endurance contributes more heavily, even though the formula will still calculate a finite result.

For consequential attempts, use qualified coaching, appropriate safety equipment, sensible progression, and current physical readiness rather than relying on a calculator alone.