One-Rep Max Calculator (Epley & Brzycki)
Estimate your one-rep max from a weight and rep count using the Epley and Brzycki formulas, plus a training percentage table, in kg or lbs.
- Estimated 1RM — Epley (kg)
- 116.7
- Estimated 1RM — Brzycki (kg)
- 112.5
- Estimated 1RM — average (kg)
- 114.6
- 90% of 1RM (kg)
- 103.1
- 80% of 1RM (kg)
- 91.7
- 70% of 1RM (kg)
- 80.2
- 60% of 1RM (kg)
- 68.8
- 50% of 1RM (kg)
- 57.3
How it works
This estimates your one-rep max (1RM) — the most you could lift for a single rep — from a lighter weight lifted for multiple reps, using two independently developed formulas: Epley's 1RM = weight × (1 + reps ÷ 30), and Brzycki's 1RM = weight × (36 ÷ (37 − reps)). Since they're separate regressions fit to different lifting data, they rarely agree exactly, so the average of the two is also shown as a practical middle estimate.
Both formulas are only reliable for roughly 1-12 reps and get progressively less accurate as fatigue and form breakdown at higher rep counts change the relationship between weight and reps — this calculator caps input at 20 reps, and Brzycki's formula is mathematically undefined at 37 reps regardless (its denominator hits zero).
The percentage table below applies common training-percentage breakpoints (90% down to 50%) to the average 1RM estimate, since programming a lift is usually done as a percentage of your max rather than the max itself.
FAQ
Why do the Epley and Brzycki estimates differ?
Each formula was derived from a different data set relating reps-to-failure to percentage of 1RM, so they're independent approximations of the same underlying relationship rather than two derivations of the same formula. The gap between them tends to widen at higher rep counts, which is part of why both formulas are considered less reliable above roughly 10-12 reps.
Is an estimated 1RM as accurate as actually testing my max?
No — these formulas are a practical estimate for programming purposes, not a substitute for an actual tested max, since individual fatigue resistance and technique at low vs. high reps varies from person to person in ways a formula fit to average data can't capture.