What is the Epley formula used for?

The Epley formula estimates one-repetition maximum (1RM) from a set of multiple repetitions performed at a submaximal load. It is commonly used in strength training to predict maximal strength without requiring a true maximal lift.

Why does the formula use a divisor of 30?

The constant 30 in the Epley formula reflects an empirical observation that each additional repetition corresponds to approximately 3.33% of the load. This linear scaling factor was derived from analysis of submaximal and maximal lift data in trained populations.

How accurate is the Epley formula?

Accuracy is highest for repetition ranges of 2–10 in compound barbell exercises. Beyond 10 reps, the formula may underestimate true 1RM because muscular endurance begins to dominate performance. Individual variation in fiber type, training history, and lifting technique also affects precision.

Can this calculator be used for all exercises?

The Epley formula was developed primarily for multi-joint barbell movements like the squat, bench press, and deadlift. It may be less accurate for isolation exercises, machine-based movements, or bodyweight exercises where leverage and stabilization demands differ.

Is a calculated 1RM the same as a tested 1RM?

No. A calculated 1RM is a mathematical estimate based on submaximal performance. Actual 1RM testing involves lifting maximal loads and is influenced by neural coordination, arousal, and skill under heavy loads—factors not captured by prediction equations.

Strength Training

One-Rep Max Calculator (Epley Formula)

Estimate your one-rep max from submaximal lifts using the classic Epley formula.

Last updated: 22 April 2026

What this tool does

This calculator estimates your one-repetition maximum (1RM) using the Epley formula, a widely used linear model published in 1985. It requires the weight lifted and the number of repetitions completed in a single set, then applies the equation 1RM = weight × (1 + reps ÷ 30) to estimate the maximum weight that can be lifted for one rep. The Epley formula is most accurate for rep ranges between 1 and 10, with reliability decreasing as repetition counts approach the validated upper limit.

Inputs

Result

—

Formula Used

1RM = w \times (1 + \frac{r}{30})

w

Weight lifted in kg

r

Reps performed

Spotted something off? Let us know — we update calculators regularly.

How One-Rep Max Calculator (Epley Formula) works

This calculator estimates a lifter's one-repetition maximum (1RM) using the Epley formula, which multiplies the weight lifted by a factor derived from the number of repetitions completed. Developed by Boyd Epley in 1985, the equation assumes a linear relationship between repetitions performed and maximal strength. The calculator returns an estimate of the heaviest weight an individual could lift for a single repetition, based on a submaximal set.

The formula

The Epley formula is expressed as:

1RM = weight × (1 + reps / 30)

Where weight is the load lifted (in kilograms or pounds), and reps is the number of repetitions completed to momentary muscular fatigue or volitional cessation. For example, lifting 100 kg for 5 repetitions yields an estimated 1RM of 100 × (1 + 5/30) = 116.7 kg.

Where this method is most accurate

The Epley formula tends to produce closer estimates when repetitions fall between 2 and 10. Performance beyond 10 repetitions shifts toward muscular endurance rather than maximal strength, and the linear assumption may underestimate true 1RM. The equation was derived from observations in trained lifters performing compound barbell exercises such as the bench press and squat. Accuracy may vary with training status, movement pattern, and whether the set is performed to true failure or stopped with repetitions in reserve.

What this tool does not do

This calculator generates a numeric estimate from a public formula. It does not prescribe training loads, diagnose strength deficits, or account for technique, fatigue, or individual recovery capacity. The result is not a recommendation to attempt a maximal lift, nor does it replace direct 1RM testing under supervision. The tool does not adjust for exercise variation, equipment differences, or concurrent training stress.

Disclaimer

This tool is for educational and informational purposes only. It does not provide medical, training, or health advice. The output is an estimate derived from a mathematical model and may not reflect actual performance. Consult a qualified strength coach or healthcare professional before modifying training protocols or attempting maximal lifts.

Questions

What is the Epley formula used for?: The Epley formula estimates one-repetition maximum (1RM) from a set of multiple repetitions performed at a submaximal load. It is commonly used in strength training to predict maximal strength without requiring a true maximal lift.
Why does the formula use a divisor of 30?: The constant 30 in the Epley formula reflects an empirical observation that each additional repetition corresponds to approximately 3.33% of the load. This linear scaling factor was derived from analysis of submaximal and maximal lift data in trained populations.
How accurate is the Epley formula?: Accuracy is highest for repetition ranges of 2–10 in compound barbell exercises. Beyond 10 reps, the formula may underestimate true 1RM because muscular endurance begins to dominate performance. Individual variation in fiber type, training history, and lifting technique also affects precision.
Can this calculator be used for all exercises?: The Epley formula was developed primarily for multi-joint barbell movements like the squat, bench press, and deadlift. It may be less accurate for isolation exercises, machine-based movements, or bodyweight exercises where leverage and stabilization demands differ.
Is a calculated 1RM the same as a tested 1RM?: No. A calculated 1RM is a mathematical estimate based on submaximal performance. Actual 1RM testing involves lifting maximal loads and is influenced by neural coordination, arousal, and skill under heavy loads—factors not captured by prediction equations.

Sources & Methodology

Applies the Epley (1985) formula: 1RM = weight × (1 + reps / 30). This linear model estimates one-repetition maximum from submaximal lift performance, using a constant divisor of 30 to scale the repetition factor.

More in Strength Training

View all 18 →