One Rep Max Calculator
What is a one rep max?
Your one rep max (1RM) is the heaviest weight you can lift once with good form. Testing it every time is tiring and risky, so this calculator estimates it from a set you have already finished: the weight you lifted and how many reps you got.
The formulas this calculator uses
Pick the formula you want. w is the weight you lifted and r is the number of reps.
| Formula | Equation | Best fit |
|---|---|---|
| Epley | 1RM = w × (1 + r ÷ 30) | Balanced. Closest around 5 to 10 reps |
| Brzycki | 1RM = w × 36 ÷ (37 − r) | Reads a little lower. Closest at 2 to 5 reps |
| Lombardi | 1RM = w × r^0.10 | Runs higher as the reps climb |
Sources: Epley (1985), Boyd Epley Workout; Brzycki (1993), JOPERD 64(1):88-90; Lombardi (1989), Beginning Weight Training.
Assumptions and limits
Every formula assumes the set went close to failure with the same technique you would use on a max attempt. Accuracy drops as reps climb, so the input stops at 12 reps. Estimates also run high on lifts with a long range of motion, such as the deadlift, and low on short single-joint moves such as curls.
How to use the result
Use the rep table to pick working weights. Strength blocks usually sit at 80 to 90% of 1RM for 2 to 5 reps, and muscle growth blocks at 65 to 80% for 6 to 12 reps. Re-estimate every few weeks, because the number moves as you get stronger.
FAQ
How accurate is a 1RM calculator?
Within about 5% for sets of 10 reps or fewer taken close to failure. The further past 10 reps you go, the more the estimate drifts.
Which formula should I use?
Epley is a safe default. Brzycki reads a little lower on heavy sets of 2 to 5 reps, and Lombardi runs higher as reps climb. Pick one and stay with it so your numbers stay comparable.
Can I use this for any exercise?
Yes, but it fits big barbell lifts best: bench press, squat, deadlift, and overhead press. On single-joint moves such as curls, treat it as a rough guide.
Do I need to test my true max?
No. Most training plans run off an estimated max. Test a real max only when you are trained for it and have a spotter.