Weight lifted, Repetitions
One Rep Max (1RM) Calculator
Estimate the most weight you could lift once from a set you have already done.
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How this calculator works
Testing a true one-rep max is tiring and carries some injury risk, so lifters estimate it from a submaximal set. The Epley and Brzycki formulas agree closely for sets of 10 reps or fewer; beyond that the estimates drift apart and become unreliable.
Formula
- Epley: 1RM = weight × (1 + reps / 30)
- Brzycki: 1RM = weight × 36 / (37 − reps)
- Training load = 1RM × percentage
Worked example
100 kg for 5 reps
- Weight lifted
- 100
- Repetitions
- 5
Result114.6 estimated 1RM
Average of Epley (116.7) and Brzycki (112.5), in the unit you entered.
Things to keep in mind
- Estimates are most reliable for sets of 2 to 10 reps taken close to failure with good form.
- Use a spotter or safety pins when lifting near your maximum.
Frequently asked questions
Which 1RM formula is more accurate?
Both are close for low reps. Brzycki tends to be a little more conservative below 10 reps and Epley a little higher. Averaging them is a reasonable working number.
How many reps should I use for the estimate?
A hard set of 3 to 6 reps gives the best estimate. Sets above 10 reps depend heavily on endurance and overstate or understate strength.
What percentage of 1RM should I train at?
As a rough guide, 85% and above for maximal strength (1-5 reps), 65-85% for muscle growth (6-12 reps) and below 65% for endurance (15+ reps).
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Results are estimates based on the values you enter and the published method shown above. They do not replace professional medical, financial or legal advice. Method reviewed October 7, 2026. About this site