One Rep Max Calculator
Free one-rep max calculator. Estimate your 1RM from any set with Epley and Brzycki formulas, plus working-set percentages. No signup.
What is a one-rep max calculator?
A one-rep max (1RM) calculator estimates the maximum weight you can lift once, from a set you can actually do — e.g. 225 lb for 5 reps. It uses formulas like Epley and Brzycki so you can program training without risking a maximal single.
How this calculator works
- Enter the weight lifted and the reps you completed to near failure.
- Epley estimates 1RM = weight × (1 + reps/30); Brzycki uses weight × 36/(37 − reps).
- It averages the two for a planning number.
- Percentage-based working weights (95% down to 50%) are generated from the estimate.
How to use the result
- Program heavy sets at 85–90% of the estimate, volume work at 60–75%.
- Re-estimate every 4–6 weeks — your real 1RM moves as you train.
- Use the estimate to pick a weight for a planned 1RM test — don’t jump straight in.
- For anything competitive, test a true 1RM under supervision rather than relying on an estimate.
How accurate is a 1RM calculator?
Within about 5–10% for sets up to 10 reps, with Epley and Brzycki both well-tested. Above 10 reps the estimates drift — formulas assume reps stay near maximal. Fatigue, technique, and bar speed also shift the real number, so treat estimates as a training guide, not a record.
Common mistakes
- Using a set that wasn’t near failure. Formulas assume you had few reps in reserve; an easy 5-rep set overestimates your 1RM.
- Extrapolating beyond 10 reps. A 20-rep set can inflate the estimate badly.
- Testing a 1RM too often. Max attempts are taxing — estimate most of the time, test occasionally.
Strength numbers pair with body-composition tracking — the lean body mass calculator shows the tissue behind the lifts, and the body fat calculator tracks the composition side of training progress.