One Rep Max Calculator — Epley, Brzycki, Lander & Mayhew

Your one-rep max is the heaviest weight you can lift for a single clean repetition of a given exercise. Coaches and lifters use it as the unit that all training percentages reference. Testing it directly is risky and demands a long warm-up and a spotter, so the standard alternative is to lift a sub-maximal weight to fatigue and predict 1RM from the load and rep count.

Four formulas dominate the strength-and-conditioning literature. Let w be the weight you used and r the number of full reps you completed:

• Epley (1985): 1RM = w × (1 + r/30)
• Brzycki (1993): 1RM = w × 36 / (37 − r)
• Lander (1985): 1RM = 100w / (101.3 − 2.67123 × r)
• Mayhew (1992): 1RM = 100w / (52.2 + 41.9 × e^(−0.055 × r))

The calculator computes all four and reports the arithmetic mean as the consensus 1RM, along with the minimum (a conservative training ceiling) and the maximum (a stretch attempt target). The spread between formulas doubles as a confidence signal — narrow spread for low rep counts, wider spread the further you push past the original fit data.

The cross-validation reference is LeSuer et al. (1997) in the Journal of Strength and Conditioning Research, which tested all four formulas against true 1RMs in the bench press, squat, and deadlift on 67 trained lifters. They found no statistically meaningful winner for reps in the 2 – 10 range — average prediction error was within three percent of the actual max for each formula. Beyond ten reps the formulas were not designed to extrapolate, and their predictions diverge; the page surfaces a low-confidence warning above 10 reps and refuses to compute past 15 reps.

Once a 1RM is estimated, the calculator builds a training-load table from the NSCA Essentials of Strength Training and Conditioning (Baechle & Earle, 4th ed., 2016). The table gives the percentage of 1RM a typical trained lifter can complete for a given rep target — 100% for one rep, 95% for two, 87% for five, 75% for ten, and so on. Loads are rounded to the nearest half kilogram or pound, which is the smallest plate jump available in most commercial gyms.

The page also runs an inverse-Epley sanity check: feed the calculated 1RM and your rep count back through w = 1RM / (1 + r/30) and the result should equal the weight you entered. This is a self-test that the arithmetic is correct, not a separate prediction.

• LeSuer, McCormick, Mayhew, Wasserstein & Arnold (1997) — The accuracy of prediction equations for estimating 1-RM performance, J. Strength Cond. Res. 11(4): 211–213
• Brzycki M (1993) — Strength testing: predicting a one-rep max from reps-to-fatigue, JOPERD 64(1): 88–90
• Mayhew, Ball, Arnold & Bowen (1992) — Relative muscular endurance performance as a predictor of bench-press strength, J. Appl. Sport Sci. Res. 6(4): 200–206
• Baechle TR & Earle RW (eds, 2016) — NSCA Essentials of Strength Training and Conditioning, 4th ed., Human Kinetics (chapters 15 and 17)
• Reynolds, Gordon & Robergs (2006) — Prediction of 1RM strength from multiple-rep maximum testing and anthropometry, J. Strength Cond. Res. 20(3): 584–592

Formulas, percent-of-1RM tables, and the accuracy bands on this page were last cross-checked against the cited publications on 2026-05-11. The page is reviewed annually and whenever a major strength-and-conditioning text updates its prescription tables.