One Rep Max Calculator — 7 Formulas & Training Loads

How this calculator works

Each formula predicts your 1RM from a weight (w) lifted for a number of reps (r):

• Epley: w × (1 + r ÷ 30)
• Brzycki: w × 36 ÷ (37 − r)
• Lander: 100 × w ÷ (101.3 − 2.67123 × r)
• Lombardi: w × r^0.10
• Mayhew et al.: 100 × w ÷ (52.2 + 41.9 × e^{−0.055 × r})
• O'Conner et al.: w × (1 + 0.025 × r)
• Wathan: 100 × w ÷ (48.8 + 53.8 × e^{−0.075 × r})

The headline is the average of all seven. In a comparison of these equations (LeSuer et al., 1997), most were reasonably accurate for sets of 10 or fewer reps, and accuracy fell as reps increased.

By Suhaib Hassan · Reviewed 28 September 2026 against the published equations and NSCA guidance · How CalculatePilot verifies formulas →

A worked example

Lifting 155 lb for 8 reps. Epley: 155 × (1 + 8 ÷ 30) = 196 lb. Brzycki: 155 × 36 ÷ 29 = 192 lb. O'Conner: 155 × 1.2 = 186 lb. The seven formulas range from about 186 to 198 lb, averaging about 193 lb. An 85% strength load would then be about 164 lb.

Using your 1RM for training

The NSCA's general guidance: strength work at about 85% of 1RM or more for 6 reps or fewer; hypertrophy at about 67–85% for 6–12 reps; muscular endurance at 67% or less for 12 or more reps. Re-estimate every 4–8 weeks as you get stronger so training weights don't become too light.

Testing a true 1RM carries more injury risk than a submaximal set — use good form, a spotter or safety bars, and don't test through pain.

Sources

• LeSuer DA, McCormick JH, Mayhew JL, et al. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res 1997;11:211–213.
• Brzycki M. Strength testing — predicting a one-rep max from reps-to-fatigue. J Phys Educ Recreat Dance 1993;64:88–90.
• Epley B. Poundage chart. Boyd Epley Workout. Lincoln, NE, 1985.
• Mayhew JL, Ball TE, Arnold MD, Bowen JC. Relative muscular endurance performance as a predictor of bench press strength in college men and women. J Appl Sport Sci Res 1992;6:200–206.
• Haff GG, Triplett NT (eds). Essentials of Strength Training and Conditioning, 4th ed. National Strength and Conditioning Association. Human Kinetics, 2016.

Frequently asked questions

Which one-rep max formula is most accurate?expand_more

No single formula wins for every lift and person. Results are closest together for low-rep sets, which is why using a set of 3–6 reps and averaging the formulas gives a steadier estimate.

How many reps should I use to estimate my 1RM?expand_more

A hard set of about 3–10 reps works best. Above 10–12 reps, the formulas diverge and become less reliable, because endurance starts to limit the set more than strength.

How often should I re-test my 1RM?expand_more

Every 4–8 weeks is common. Re-estimating from a recent hard set is safer than a true max attempt and keeps your training percentages up to date.