How to use
- After warming up, lift a weight for as many good reps as you can. 10 reps or fewer gives the best estimate.
- Choose kg or lb, then enter the weight and the reps you completed.
- See your estimated one rep max (1RM), each formula’s answer and your training loads.
One rep max formulas
Here w is the weight lifted and r the number of reps.
| Formula | 1RM equals |
|---|---|
| Epley (1985) | w × (1 + r ÷ 30) |
| Brzycki (1993) | w × 36 ÷ (37 − r) |
| Lander (1985) | w ÷ (1.013 − 0.0267123 × r) |
| Lombardi (1989) | w × r^0.10 |
| Mayhew et al. (1992) | w ÷ (0.522 + 0.419 × e^(−0.055 × r)) |
| O’Connor et al. (1989) | w × (1 + 0.025 × r) |
| Wathen (1994) | w ÷ (0.488 + 0.538 × e^(−0.075 × r)) |
Your result is the average of all seven. A single rep is already a 1RM, so 1 rep returns the weight you lifted.
Examples
- 100 kg for 5 reps: the formulas range from 112.5 kg (Brzycki, O’Connor) to 119 kg (Mayhew). The average is 115.5 kg.
- 225 lb for 5 reps: about 259.9 lb, with a range of 253.1 to 267.8 lb.
- At 10 reps, Epley and Brzycki agree exactly: 100 kg × 10 gives 133.3 kg with both.
Training loads from a 115.5 kg 1RM
| % of 1RM | Load | Reps (about) | Best for |
|---|---|---|---|
| 100% | 115.5 kg | 1 | Strength |
| 90% | 103.9 kg | 3 | Strength |
| 85% | 98.2 kg | 5 | Strength |
| 80% | 92.4 kg | 8 | Muscle size |
| 75% | 86.6 kg | 10 | Muscle size |
| 70% | 80.8 kg | More than 10 | Muscle size |
| 65% | 75.1 kg | More than 10 | Endurance |
The training focus follows NSCA guidance: 4–6 reps at 85% or more for strength, 6–12 reps at 67–85% for muscle size, and 12 or more reps below 67% for endurance.
How accurate is it?
- Estimates work best from a set of 2 to 10 reps. Longer sets can overestimate.
- For the back squat and power clean, keep the set to about 5 reps, because form breaks down as you tire.
- In the examples above the seven formulas differ by about 6 to 8%, which is why we show the range.
Rounding, rep limits and formula details
Published versions of Epley and Brzycki use 4-decimal coefficients (0.0333 and 1.0278 − 0.0278 × r). We use the exact fractions they round, which differ by under 0.03% for 1 to 10 reps.
We accept up to 20 reps. Brzycki’s formula breaks down at 37 reps and Lander’s at about 38.
The reps column works the average formula backwards and rounds down. It stops at 10, where the formulas stop being reliable.
Safety
Warm up with light sets first, then heavier sets of fewer reps. Use good technique and a spotter for heavy lifts. If you train alone, estimating from a set of reps avoids a maximal attempt.
Lifting in pounds at a kg gym? Use the weight converter.