The Epley Formula: How to Calculate 1RM (With Examples)
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TL;DR: The Epley formula — 1RM = weight × (1 + reps ÷ 30) — is the most widely used 1RM equation in gym apps and the NSCA’s textbooks. It’s most accurate for squats and lower-body lifts (~3% error in testing) and works best with 2–10 rep sets. Weaknesses: slight overshoot at 1 rep, optimism past 10 reps.
What Is the Epley Formula?
1RM = weight × (1 + reps ÷ 30)
Published by Boyd Epley in 1985. Every rep adds 1/30th (3.33%) of the weight to your estimated max — simple enough to do in your head between sets, which is half the reason it’s everywhere.
How Do You Use the Epley Formula?
Pounds: bench 225 lb × 5 reps → 225 × (1 + 5/30) = 225 × 1.1667 = 262.5 lb.
Kilograms: squat 100 kg × 5 reps → 100 × 1.1667 = 116.7 kg.
Mental-math shortcut: multiply weight × reps, divide by 30, add the weight. 225 × 5 = 1125; ÷ 30 = 37.5; + 225 = 262.5. Or skip it — our one rep max calculator runs Epley plus six other formulas.
When Is Epley Most Accurate?
- Squats and lower body: lowest error of any formula in D-I football testing (~3%); confirmed by LeSuer et al. (1997).
- Low-rep sets (2–5): like every formula, best from heavy sets. A 3-rep input beats a 10-rep input.
- General use: the safest default when you don’t know which formula fits — why apps and the NSCA standardized on it.
What Are Epley’s Limitations?
The 1-rep overshoot: 100 × (1 + 1/30) = 103.3 — a baked-in ~3% optimism from the linear form. High-rep optimism: past 10 reps, +3.33%/rep compounds into generous estimates (the seven formulas diverge by 32.5 kg at 15 reps). Deadlift: underestimates like all formulas (9–14%) — add 5–10% mentally.
Epley vs Brzycki: Quick Comparison
| Epley | Brzycki | |
|---|---|---|
| Equation | w × (1 + r/30) | w × 36/(37 − r) |
| 100 kg × 5 | 116.7 kg | 112.5 kg |
| 100 kg × 10 | 133.3 kg (identical!) | |
| 100 kg × 1 | 103.3 kg (overshoots) | 100.0 kg (honest) |
| Best for | Squat, general use | Bench press, low reps |
| Past 12 reps | Optimistic but bounded | Unstable |
Full breakdown: 7 formulas compared.
Frequently Asked Questions
Is the Epley formula accurate?
For 2–10 rep sets on compound lifts, yes — within a few percent, and the most accurate formula tested on squats (~3% error). Accuracy degrades past 10 reps like all formulas.
Who is Boyd Epley?
The pioneering strength coach at the University of Nebraska, considered a founder of modern collegiate strength and conditioning. Published the formula in 1985; it’s been in the NSCA’s Essentials of Strength Training and Conditioning ever since.
Can I use Epley for dumbbell exercises?
Yes — enter the total weight (both dumbbells combined). Just be consistent about it.
Why do apps use Epley instead of the others?
Simplicity and validation: one multiplication, best-tested on squats, verifiable mentally. Good apps (including ours) show Epley alongside the other six.
Sources
- Epley, B. (1985). Original 1RM prediction equation.
- LeSuer, D.A. et al. (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).
- Haff, G.G. & Triplett, N.T. (Eds.). Essentials of Strength Training and Conditioning (4th ed.). NSCA / Human Kinetics.