Wathan one-rep max calculator
The Wathan formula estimates the weight you could lift once from a set you actually completed. All such formulas drift above about ten reps.
Estimated one-rep max
116.6kg
- 95% — about 2 reps
- 110.8
- 90% — about 4 reps
- 104.9
- 85% — about 6 reps
- 99.1
- 80% — about 8 reps
- 93.3
- 70% — about 12 reps
- 81.6
- 60% — about 20 reps
- 69.9
Show the working
- Weight lifted = 100
- Repetitions completed = 5
- Estimated one-rep max = 100 * 100 / (48.8 + 53.8*exp(-0.075*5)) = 116.583
- 95% — about 2 reps = 116.583 * 0.95 = 110.753
- 90% — about 4 reps = 116.583 * 0.90 = 104.924
- 85% — about 6 reps = 116.583 * 0.85 = 99.0951
- 80% — about 8 reps = 116.583 * 0.80 = 93.266
- 70% — about 12 reps = 116.583 * 0.70 = 81.6078
- 60% — about 20 reps = 116.583 * 0.60 = 69.9495
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- Wathan: 1RM = 100 w / (48.8 + 53.8 e^(-0.075 reps))
- w is the weight lifted and reps the number of repetitions completed to technical failure.
Estimates are only meaningful when the set was genuinely taken close to failure with good form.
The formulas agree closely at 3 to 5 reps and diverge sharply above 10.
This is a population formula, not a diagnosis. Individual metabolism, body composition and medical history all move the real answer, so treat the number as a starting point and talk to a clinician about anything that matters.