One-Rep Max Calculator
Testing a true one-rep max is risky and exhausting. Instead, lift a weight for reps and let the Epley formula estimate your 1RM — then use the percentage table below to program every working set.
Most accurate for sets of 10 reps or fewer. Estimates, not guarantees — always use safeties or a spotter near your max.
The Epley formula
Published by Boyd Epley in 1985, it’s the most widely used 1RM estimator in strength programming. It assumes each rep beyond the first costs roughly 1/30th of your max — remarkably accurate for sets under ~10 reps.
How to use the percentage table
- 90%+: heavy singles and peaking — low reps, full recovery.
- 80–90%: the strength zone — sets of 2–5.
- 60–80%: the hypertrophy zone — sets of 6–12 for muscle growth.
Re-test or re-estimate every 4–8 weeks as you get stronger.
Frequently asked questions
What is a one-rep max?
The heaviest weight you can lift for a single repetition with good form. It’s the reference point for programming training intensity.
How accurate is the Epley formula?
Very good for sets of 10 or fewer reps (usually within ~5%). Accuracy falls off with high-rep sets, where muscular endurance skews the estimate.
Should I actually test my true 1RM?
Not necessary for most lifters — estimates are safer and sufficient for programming. Competitive powerlifters test under controlled conditions.
What’s the difference between Epley and Brzycki?
Both estimate 1RM from reps; they agree closely under 10 reps. Epley (used here) is slightly more common in modern programming.
How often should I retest?
Every 4–8 weeks, or whenever your working sets start feeling easy across the board.