One Rep Max Calculator
Estimate your one-repetition maximum (1RM) from a completed set, compare seven formulas, and create a rounded training-percentage table. Bench press, squat, deadlift, and other exercises use the same calculation.
| Formula | Estimated 1RM | Difference from average |
|---|
| Percentage | Calculated load | Rounded load |
|---|
How this one rep max calculator works
Enter a weight you lifted and the number of clean repetitions you completed. The calculator estimates the heaviest load you could lift once under similar conditions. Selecting “Average of seven formulas” reduces dependence on a single equation; the comparison table shows how much the individual estimates differ.
Example: 225 lb for 5 repetitions produces a seven-formula average of about 259.9 lb, with individual estimates from about 253.1 to 267.8 lb. The same average estimates an 8-rep load of about 208.4 lb before rounding.
When the completed set is one repetition, every formula returns the entered weight. For higher-repetition sets, the result is an estimate rather than a measured maximum. Estimates are generally more useful from lower-repetition sets and can change with exercise selection, technique, tempo, fatigue, and training experience.
Formulas used
In the equations below, w is the lifted weight and r is the completed repetition count.
- Epley: 1RM = w × (1 + r ÷ 30)
- Brzycki: 1RM = w × 36 ÷ (37 − r)
- Lander: 1RM = 100w ÷ (101.3 − 2.67123r)
- Lombardi: 1RM = w × r0.10
- Mayhew: 1RM = 100w ÷ (52.2 + 41.9e−0.055r)
- O’Conner: 1RM = w × (1 + 0.025r)
- Wathan: 1RM = 100w ÷ (48.8 + 53.8e−0.075r)
The selected estimate builds the percentage table. For a target repetition count, each equation is algebraically reversed; the average option averages the seven reversed loads.
Limits and safe use
Do not treat an estimated 1RM as an instruction to attempt a maximum lift. Use appropriate warm-ups, safety arms or spotters, sound technique, and qualified coaching when needed. Stop if you feel pain, dizziness, or unusual discomfort.
This tool accepts 1–20 repetitions, but prediction error usually grows as the set moves farther from a true maximum. It does not account for exercise-specific fatigue, equipment, range of motion, body mass, injury history, or medical conditions.