What a one rep max is
Your one rep max (1RM) is the heaviest weight you can lift once with good form in a given exercise, such as the squat, bench press or deadlift. Many strength programs prescribe work as a percentage of 1RM, for example three sets of five at 80%. Testing a true max is tiring and carries some risk, so most lifters estimate it from a heavier set of several reps instead.
How to use the calculator
- Choose lb or kg.
- Enter the weight lifted in a recent hard set.
- Enter the reps you completed with good form, from 1 to 12.
- Press Calculate. The result shows the estimate from each formula and their average, and the Details card lists training weights from 50% to 100% of that average.
The formulas
With w as the weight lifted and r as the reps:
- Epley: w × (1 + r / 30)
- Brzycki: w × 36 / (37 − r)
- Lombardi: w × r^0.10
- O'Conner: w × (1 + 0.025 × r)
Each formula was fitted to a different group of lifters, so they give slightly different answers. The calculator averages the four to smooth out their differences. With a single rep, the weight you lifted is already your max, so every formula returns it unchanged.
Worked example
You bench 100 kg for 5 reps:
- Epley: 100 × (1 + 5 / 30) = 116.7 kg
- Brzycki: 100 × 36 / 32 = 112.5 kg
- Lombardi: 100 × 5^0.10 = 117.5 kg
- O'Conner: 100 × 1.125 = 112.5 kg
- Average: about 114.8 kg
At 85% of that max you would train with about 97.6 kg, a weight most people can lift for roughly five or six reps.
Good to know
- Estimates are most accurate from sets of about 3 to 8 reps. Above 10 reps the formulas drift apart, and the calculator warns you.
- Use a set taken close to failure. A set stopped well short of failure underestimates your max.
- Muscular endurance differs between people and between exercises, so the typical rep counts in the table are only a guide.
- Results are estimates, not medical or training advice. Use a spotter or safety bars when you work near your max, and stop if you feel pain.