Epley Formula: 1RM Calculator and Complete Guide

History and origin

Boyd Epley developed his formula in 1985 while serving as the first full-time strength and conditioning coach at the University of Nebraska. He was working with college football players and needed a fast, accurate way to predict maximum loads from submaximal test sets without subjecting athletes to true 1RM attempts during the season. The formula assumes a linear inverse relationship between weight and repetitions, with each rep representing approximately 3.33% of one-rep max. Despite being one of the simpler models, it has remained the most widely used 1RM equation in strength and conditioning for over forty years because of its intuitive math and reliable accuracy in the 2-10 rep range.

How to use the Epley formula (step by step)

1. Perform a heavy submaximal set. Perform a clean set of 2-10 reps to near-failure (RPE 8-9) on the lift you want to test. Record the weight and the rep count.
2. Apply the Epley equation. 1RM = weight × (1 + reps / 30)
3. Read the estimated 1RM. The output is your estimated 1RM. For programming, multiply by 0.9 to derive your Training Max — this absorbs daily strength variability and reduces overshoot risk.
4. Cross-check against other formulas. Run the same numbers through every other formula and compare. The main calculator does this automatically using a trimmed mean.

How Epley compares to the other six formulas

The same submaximal set — 225 lb × 5 reps — produces different 1RM estimates depending on which formula you use. Here are all seven, side by side:

See the full formula comparison page for accuracy data and decision-making guidance.

Validation research

The Epley formula has been evaluated in multiple peer-reviewed studies of 1RM prediction accuracy. Selected findings:

Boyd Epley: the man behind the formula

Boyd Epley was hired by the University of Nebraska in 1969 as the first full-time strength and conditioning coach in collegiate sports. He spent 35 years with Nebraska football, contributing to the program's five national championships and three Heisman trophies during the Tom Osborne era. His work helped legitimize S&C as a profession; before Epley, strength training in college sports was either coach-improvised or non-existent.

Epley founded the National Strength and Conditioning Association (NSCA) in 1978 and served as its first president. The organization now has over 60,000 members and certifies the Certified Strength and Conditioning Specialist (CSCS) credential — the standard professional certification for S&C coaches worldwide. He was inducted into the NSCA Hall of Fame in 1993 and remains a Hall of Fame Lifetime Achievement honoree.

Epley's 1985 formula — published originally as a simple poundage chart for Nebraska football players — was empirical, not derived from a peer-reviewed study. He had decades of in-house data on athletes performing reps-to-fatigue with submaximal weights, and the linear approximation 1RM = w × (1 + r/30) fit that data well enough to use as a daily training tool. Its simplicity is a feature: any coach can compute it on a clipboard during a session.

Why Epley remained dominant for 40 years

Despite the publication of more sophisticated formulas — Brzycki (1993), Mayhew (1992), Wathan (1994) — Epley remains the most widely used in coaching practice. Three reasons:

1. Mental math. Epley is the only major formula a coach can solve in their head: “225 for 5? Add 33 lb (1/30 × 5 × 225 = 37.5), call it 263.”
2. Adoption inertia. Epley was in Nebraska's training manuals before Brzycki existed. Three generations of collegiate strength coaches learned it first; many never bothered to switch.
3. Adequate accuracy in the common case. For sets of 4-8 reps — the bread-and-butter rep range for most non-powerlifting training — Epley is within 2-3% of Brzycki and Mayhew. The marginal accuracy gain doesn't justify switching.

When Epley fails

The linear assumption — each rep = ~3.33% of 1RM — breaks down at the extremes. Two specific failure modes:

Epley in modern programming

Epley is used implicitly even by lifters who don't recognize the name:

• 5/3/1 Training Max. Wendler's 5/3/1 program uses TM = 90% of 1RM. The 1RM is typically calculated from a Week 3 AMRAP set using Epley (e.g., 8 reps at 95% TM → estimated new 1RM via Epley → adjust TM upward).
• Linear progression resets. When a novice on Starting Strength stalls, the standard 90% reset is computed against an Epley-estimated 1RM from the most recent successful set.
• App-driven training. Most popular training apps (Strong, Boostcamp, etc.) default to Epley for their built-in 1RM estimator because of its computational simplicity.

References

1. Original publication: Epley, B. (1985). Poundage chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises.
2. LeSuer et al. (1997): LeSuer, D.A., McCormick, J.H., Mayhew, J.L., Wasserstein, R.L., & Arnold, M.D. (1997). The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research, 11(4), 211-213.
3. Reynolds et al. (2006): Reynolds, J.M., Gordon, T.J., & Robergs, R.A. (2006). Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. Journal of Strength and Conditioning Research, 20(3), 584-592.
4. Wood et al. (2002): Wood, T.M., Maddalozzo, G.F., & Harter, R.A. (2002). Accuracy of seven equations for predicting 1-RM performance of apparently healthy, sedentary older adults. Measurement in Physical Education and Exercise Science, 6(2), 67-94.
5. Wikipedia: One-repetition maximum — general reference for 1RM prediction equations.
6. Essentials of Strength Training and Conditioning (NSCA, Human Kinetics) — NSCA CSCS textbook chapter on load assignment.