What is the One Rep Max Calculator?
The one rep max calculator estimates the heaviest weight you could lift once, based on a lighter set of several reps. It helps you plan training loads safely.
How to use the One Rep Max tool
- Enter Weight lifted and Reps completed.
- The result updates instantly as you type, or press Calculate.
- Use Try an example to see how it works, and Reset to start again.
Formula
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). The tool averages both.
Worked example
With weight lifted 80 kg, reps completed 5, the estimated 1rm comes to 91.7. Epley: 93.3; Brzycki: 90; 80% of 1RM: 73.3.
Frequently asked questions
Are low reps more accurate?
Yes. Estimates are most reliable for sets of 10 reps or fewer.
Is it safe to test a true 1RM?
Use a spotter and good form, or rely on the estimate to avoid injury.
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Checked by Calcovate · Formula tested against worked examples · Updated 7 Nov 2026 · How we check our calculators. General information only, not financial or medical advice.