One Rep Max Calculator
Estimate your one-rep max from a set you've actually done — then use the percentage table to program your training loads.
| % of 1RM | Weight | Typical reps |
|---|
The formulas
Brzycki: 1RM = weight × 36 ÷ (37 − reps)
225 lb × 5 reps → Epley: 225 × (1 + 5/30) = 262 lb. Brzycki gives ≈ 253 lb — close agreement at low reps.
100 kg × 12 reps (above the accurate 10-rep guideline, shown deliberately):
Epley: 100 × (1 + 12/30) = 100 × 1.4 = 140 kg. Brzycki: 100 × 36 ÷ (37 − 12) = 3,600 ÷ 25 = 144 kg. Averaged, this calculator would report about 142 kg.
The two formulas now differ by 4 kg (about 3%), versus roughly 9 lb (3.4%) at 5 reps in the example above — both are similar percentage gaps, but the 12-rep set sits past the point where the estimate is considered reliable, since a longer set is increasingly limited by endurance rather than raw strength.
Training with percentages
| % 1RM | Reps | Focus |
|---|---|---|
| 100% | 1 | Max strength |
| 90% | 3–4 | Strength |
| 80% | 6–8 | Strength + size |
| 70% | 10–12 | Hypertrophy |
| 60% | 15+ | Endurance |
Estimating your max from a submaximal set is safer than testing a true one-rep max, especially for beginners. Keep the test set at 10 reps or fewer for accuracy — beyond that, endurance clouds the strength estimate. Use the percentages to auto-set working weights (e.g. "5×5 at 80%"), and re-estimate every few weeks as you get stronger. Track your training energy needs with the calories burned and protein calculators.
Other 1RM formulas in use
| Formula | Equation | Notes |
|---|---|---|
| Epley | weight × (1 + reps ÷ 30) | Used on this page; simple, widely applied |
| Brzycki | weight × 36 ÷ (37 − reps) | Used on this page; slightly more conservative at higher reps |
| Lombardi | weight × reps0.10 | Older formula, common in strength literature |
| Mayhew et al. | weight × 100 ÷ (52.2 + 41.9 × e−0.055 × reps) | Derived from bench press research; more complex |
No formula is exactly right for every lifter or every lift — they're all curve fits to average data from research subjects. Averaging Epley and Brzycki, as this calculator does, smooths out some of the disagreement between individual formulas without adding much complexity.
Common 1RM testing mistakes
- Testing sets well past 10-12 reps. As the higher-rep worked example above shows, the formulas start to diverge more once endurance rather than strength limits the set.
- Applying the same formula confidence to every exercise. These formulas were validated mainly on bench press and squat; expect less accuracy on smaller, stabilizer-heavy, or single-joint movements.
- Re-testing right after a hard training block or without a deload. Residual fatigue lowers the set's true ceiling, so the resulting estimate will read lower than your actual current capacity.
Frequently asked questions
How do I calculate my one-rep max?
Epley: weight × (1 + reps/30). 225×5 ≈ 262 lb. Best at ≤10 reps.
Which formula is most accurate?
Epley and Brzycki agree closely at low reps; all lose accuracy above ~10–12 reps.
Why use 1RM percentages?
Programs prescribe loads as % of 1RM, so estimating it sets training weights without maxing out.
Why do formulas disagree more at higher rep counts?
Each formula is fit to real data, and those curves spread apart as reps climb because endurance, not strength, starts limiting the set. Expect roughly 1-2% disagreement at 5 reps versus 3%+ by 12 reps.
Do these formulas work for every exercise?
They're most accurate for large compound lifts like bench press and squat, since that's the data they were built from — expect less reliability on smaller, stabilizer-heavy movements.
Related calculators
Medical disclaimer: An estimate for training, not medical advice. Lift with proper form and a spotter for heavy attempts; consult a professional if you have injuries or health conditions. Formulas: Epley & Brzycki. Last reviewed: September 2026.