Free tool
One-rep max calculator
Your one-rep max (1RM) is the heaviest weight you could lift for a single rep. Enter any hard set — the weight and the reps you completed — and this calculator estimates your 1RM with four standard formulas, plus the training percentages that follow from it.
Estimated one-rep max
115 kg
Epley: 116.5 kgBrzycki: 112.5 kgLombardi: 117.5 kgO'Conner: 112.5 kg
| % of 1RM | Weight | Typical use |
|---|---|---|
| 95% | 109 kg | ~2 reps · strength |
| 90% | 103.5 kg | ~4 reps · strength |
| 85% | 97.5 kg | ~6 reps · strength |
| 80% | 92 kg | ~8 reps · hypertrophy |
| 75% | 86 kg | ~10 reps · hypertrophy |
| 70% | 80.5 kg | ~12 reps · hypertrophy |
| 65% | 74.5 kg | ~15 reps · endurance |
How the estimate works
All 1RM formulas convert a multi-rep set into a single-rep equivalent. They are most reliable when the set was 10 reps or fewer and taken close to failure — above ~10 reps the formulas diverge and the estimate gets softer. This page shows the average of four published formulas and each formula's individual result, so you can see the spread.
| Formula | Definition | Character |
|---|---|---|
| Epley (1985) | 1RM = w × (1 + r ÷ 30) | The most common default; slightly higher estimates at high reps. |
| Brzycki (1993) | 1RM = w × 36 ÷ (37 − r) | Close to Epley below 10 reps; conservative above. |
| Lombardi | 1RM = w × r^0.10 | Power-curve fit; conservative at moderate reps. |
| O'Conner | 1RM = w × (1 + 0.025 × r) | The most conservative of the four. |
w = weight lifted, r = reps completed. With r = 1 the set already is a measured 1RM.
Why train off percentages?
Most strength programs prescribe loads as a percentage of 1RM: heavy triples around 90%, fives around 85%, hypertrophy work between 65% and 80%. Estimating your 1RM from a recent hard set — instead of maxing out — gives you those working weights without the fatigue and injury risk of an actual max attempt. Re-estimate every few weeks as your training log shows progress, and your percentages keep pace with your strength.
Track it instead of recalculating it
Reysa logs every set and shows your strength trend over time — free on iPhone.