One-rep max (1RM) calculator

How the estimate is calculated

A one-rep max (1RM) is the heaviest load you can lift once with your normal technique. Testing it directly is a skill and takes a fresh day, so most lifters estimate it from a heavier set of a few reps. This calculator uses two of the most widely cited equations, where w is the weight and r is the number of reps you could do before failing:

• Epley: 1RM = w × (1 + r ÷ 30)
• Brzycki: 1RM = w × 36 ÷ (37 − r)

The headline number is the midpoint of the two. In a study of 220 men bench pressing, Mayhew and colleagues found Brzycki the most accurate single equation when sets went to 10 reps or fewer, and noted that averaging two equations may reduce error. Below about 10 reps the two formulas agree closely (they are identical at exactly 10). The gap you see is a reminder that equations make different assumptions; it is not a confidence interval.

Worked example

Say you squatted 100 kg for 5 reps and the fifth rep was your limit. Epley gives 100 × (1 + 5 ÷ 30) = 116.7 kg. Brzycki gives 100 × 36 ÷ 32 = 112.5 kg. The estimate is the midpoint, 114.6 kg (about 252.6 lb). At 80% of that estimate you would load 91.7 kg, which rounds to 92.5 kg on a bar with 1.25 kg plates.

Why one rep returns the weight you entered

With one rep and no reps in reserve, the calculator reports the weight you entered and applies no formula; raw Epley would add 3.3%. That number is your 1RM for the day only if the single really was the heaviest you could lift. A comfortable single is not a tested max.

Reps in reserve

Both formulas assume the set went to failure. If you stopped with reps left, choose how many. The calculator adds them to your reps (3 reps with 2 left counts as 5 to failure). That is a practical approximation: people often misjudge how many reps they had left, especially on lighter, higher-rep sets. Read RPE and reps in reserve for how to calibrate it.

When the estimate misleads

• High reps. Accuracy fell beyond 10 reps in Mayhew and colleagues' bench press data, and Reynolds and colleagues concluded that no more than 10 reps should be used, with 5-rep maxes predicting best in their chest and leg press testing. This tool stops at 12 and warns above 10.
• Different lifts and lifters. In LeSuer and colleagues' test of seven equations on untrained students, every equation underestimated the deadlift, and most differed from the tested bench press and squat. People also vary in how many reps they can do at a given percentage of their max (Nuzzo and colleagues pooled 952 such tests), so any formula is an average.
• Technique changes near the limit. A grinding single usually looks different from rep five of a set. If your form breaks on heavy singles, a tested max will come in under the estimate.
• Fatigue and the day. Sleep, food, stress and the work you did before the set all move the result.
• Olympic lifts. Snatches and clean and jerks are limited by speed and positions, not grinding strength. Do not use a rep-based estimate for them.

Using the number in training

Most programs prescribe work as a percentage of a max. Some use your estimated 1RM directly; others, such as 5/3/1, use a deliberately lower training max. Check which number your program means before you load the bar. Our guide to training max vs one-rep max walks through the difference. To load the bar quickly, use the plate calculator; to see how a lift compares with competition results, try the strength standards tool.

If you want to test a true max, do it with a spotter or safety arms, build up with warm-up singles, and stop when bar speed or technique drops. A coach who can see you lift is the best judge of when a heavy attempt is sensible. If you have an injury or a medical condition, ask a qualified professional first.

FAQ

Which formula is the most accurate?

No single formula wins for every lift and lifter. Epley and Brzycki are close for low-rep sets and identical at 10 reps. Showing both, and their midpoint, is more honest than picking one.

Is my estimated 1RM a weight I should attempt?

No. It is a planning number. A tested max depends on skill with heavy singles, the day, and safety equipment. Many lifters never need to test one.

Can I enter pounds?

Yes. Switch units at the top; results are shown in both. Conversions use the exact definition 1 lb = 0.45359237 kg.

Does the calculator store my numbers?

No. The math runs in your browser. Inputs are not sent anywhere, not added to the page address, and never included in analytics.

Sources

• Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance. 1993;64(1):88–90. doi:10.1080/07303084.1993.10606684 (the Brzycki equation).
• Epley B. Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985. A coaching chart rather than a research paper; the equation is cited in the studies below.
• Mayhew JL, Prinster JL, Ware JS, Zimmer DL, Arabas JR, Bemben MG. Muscular endurance repetitions to predict bench press strength in men of different training levels. J Sports Med Phys Fitness. 1995;35(2):108–113. PubMed 7500624 (accuracy at ≤10 reps; averaging equations).
• Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. J Strength Cond Res. 2006;20(3):584–592. doi:10.1519/R-15304.1 (use 10 reps or fewer; 5RM predicted best).
• LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res. 1997;11(4):211–213. doi:10.1519/00124278-199711000-00001 (equations underestimated the deadlift).
• Nuzzo JL, Pinto MD, Nosaka K, Steele J. Maximal number of repetitions at percentages of the one repetition maximum: a meta-regression and moderator analysis of sex, age, training status, and exercise. Sports Med. 2024;54(2):303–321. doi:10.1007/s40279-023-01937-7 (between-person variation in reps at a given %1RM).

Method and copy last reviewed Oct 20, 2026. See our editorial policy. Educational information, not medical or coaching advice.