Health & Medicine · Fitness · Strength Training
Epley One Rep Max Calculator
Estimates your one-repetition maximum (1RM) from a submaximal lift using the Epley formula.
Calculator
Formula
w = weight lifted (kg or lb), r = number of repetitions performed. The formula estimates the maximum weight you could lift for a single repetition based on a submaximal effort.
Source: Epley, B. (1985). Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises. Cited in Baechle & Earle, Essentials of Strength Training and Conditioning, NSCA, 2000.
How it works
The Epley formula — 1RM = w × (1 + r/30) — was published by Boyd Epley in 1985 and remains one of the most cited predictive equations in resistance training literature. You simply enter the weight you lifted and the number of consecutive repetitions you completed, and the formula projects what you could have lifted for exactly one rep.
The formula assumes a roughly linear relationship between load and repetitions in the range of 1–10 reps. Each additional repetition beyond one is treated as representing approximately 1/30th of additional capacity. Because fatigue, technique, and individual recovery profiles vary, the result is an estimate rather than a guaranteed true maximum.
Coaches and athletes use the estimated 1RM to set percentage-based training zones. For example, strength development typically occurs at 85–95% of 1RM for 1–5 reps, while hypertrophy work is often programmed at 65–80% for 6–12 reps. The percentage breakdown provided by this calculator makes it straightforward to structure an entire training block from a single submaximal test set.
Worked example
Example: Back Squat
An athlete squats 120 kg for 6 repetitions. Applying the Epley formula:
1RM = 120 × (1 + 6/30) = 120 × (1 + 0.2) = 120 × 1.2 = 144 kg
From this estimated 1RM, the loading chart would be:
- 95% → 136.8 kg
- 90% → 129.6 kg
- 85% → 122.4 kg
- 80% → 115.2 kg
- 75% → 108.0 kg
- 70% → 100.8 kg
The athlete can now program their next training block without performing a risky true 1RM test.
Limitations & notes
The Epley formula becomes less accurate as reps increase beyond 10, since fatigue and muscular endurance play a greater role. For best accuracy, use a weight that allows between 2 and 6 clean repetitions. The formula also does not account for individual factors such as training age, fiber type distribution, or exercise-specific technique. Results will vary between exercises — a 1RM estimated from a Romanian deadlift set will not necessarily transfer to a conventional deadlift. The calculator is intended for general programming guidance only and should not replace supervised maximal testing for competitive powerlifting or clinical assessment contexts.
Frequently asked questions
How accurate is the Epley formula compared to a true 1RM test?
Research generally shows the Epley formula is accurate within 5–10% when the submaximal set is performed with 3–6 reps. Accuracy decreases as rep count rises above 10, where muscular endurance begins to confound the estimate. For competitive use, a supervised maximal test is still the gold standard.
Should I use kilograms or pounds in the calculator?
The Epley formula is unit-agnostic — simply enter weight in whichever unit you prefer (kg or lb) and the output will be in the same unit. Just be consistent: do not mix kilograms and pounds in the same calculation.
Why is the formula less accurate above 10 reps?
At higher rep ranges, muscular endurance, cardiovascular fatigue, and lactate accumulation become significant limiting factors. The Epley formula assumes a near-linear strength-to-rep relationship, which breaks down when endurance is the primary constraint rather than raw strength. For rep counts above 10, formulas like the Brzycki or O'Conner equations may provide slightly better estimates, though all predictive formulas share this limitation.
Can I use this calculator for any exercise?
Yes, the formula is exercise-independent and can be applied to the squat, bench press, deadlift, overhead press, or any other barbell or machine lift. However, keep in mind that your 1RM estimated from one exercise does not directly predict your 1RM on a different movement. Each exercise should be tested or estimated separately.
What percentage of my 1RM should I use for different training goals?
General evidence-based guidelines from the NSCA suggest: maximal strength — 85–100% for 1–5 reps; hypertrophy — 65–85% for 6–12 reps; muscular endurance — below 65% for 15 or more reps. The percentage breakdown in this calculator directly supports these programming zones.
How does the Epley formula differ from the Brzycki formula?
The Brzycki formula is 1RM = w / (1.0278 - 0.0278 × r). Both are commonly used 1RM prediction equations, and they produce very similar results for rep ranges of 2–8. The Epley formula tends to predict slightly higher 1RMs at higher rep counts. Neither is universally more accurate; the choice is often one of convention or coaching preference.
Last updated: 2025-01-30 · Formula verified against primary sources.