One Rep Max Calculator
Estimate your one-rep max (1RM) — the maximum weight you could lift for a single repetition — from a set you've already done. Enter the weight and reps to get your 1RM plus a percentage table for planning your training loads.
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Estimates are most accurate for sets of 1–10 reps. Always warm up and use a spotter when testing heavy loads.
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Save ⟶How to use the One Rep Max Calculator
- 1Enter the weight you lifted for your working set.
- 2Enter how many clean repetitions you completed (best accuracy at 1–10 reps).
- 3Read your estimated 1RM (average of the Epley and Brzycki formulas).
- 4Use the percentage table to set loads for strength, hypertrophy and endurance work.
How 1RM is estimated
Testing a true one-rep max is risky and tiring, so lifters estimate it from a sub-maximal set instead. This calculator averages two well-known formulas: Epley (weight × (1 + reps/30)) and Brzycki (weight × 36 / (37 − reps)). Both are most accurate when the set is 10 reps or fewer, because higher-rep sets depend more on endurance than pure strength.
Your estimated 1RM is the foundation of percentage-based training: strength work typically uses 85–95% of 1RM for low reps, hypertrophy 67–85% for moderate reps, and muscular endurance below 67% for higher reps.
Frequently Asked Questions
▸How accurate is a 1RM estimate?
Very good for sets of 1–6 reps and still useful up to 10. Beyond that, accuracy drops because high-rep performance reflects endurance more than maximal strength.
▸How often should I test my max?
Re-estimating every 4–8 weeks from your working sets is plenty. Maxing out for real is best reserved for occasional planned tests with proper warm-up and a spotter.