One rep max calculator
Enter the weight you lifted and the repetitions you finished to estimate the heaviest single lift you could do. Four equations give four estimates, and the answer averages them.
This answer is for the example values in the boxes above. 185 lb for 5 repetitions. Change the boxes to see your own answer.
This is an estimate for planning, not a test of your strength and not training advice.
How many repetitions a share of your one rep max allows differs from person to person and from lift to lift.
How it works
The calculator applies four published equations to the weight and the repetitions. With w the weight and r the repetitions, they are:
- Epley: 1RM = w × (1 + r / 30)
- Brzycki: 1RM = w × 36 / (37 - r)
- Mayhew: 1RM = 100 × w / (52.2 + 41.9 × e^(-0.055 × r))
- Wathen: 1RM = 100 × w / (48.8 + 53.8 × e^(-0.075 × r))
The answer averages the four. It also gives the weight at each 5 percent from 95 down to 50 percent of that average.
A worked example
A lifter does 5 repetitions with 185 pounds. Epley gives 215.8 pounds, Brzycki 208.1, Mayhew 220.2 and Wathen 215.7, so the estimate is 215.0 pounds. Ninety-five percent of that is 204.2 pounds, and 50 percent is 107.5 pounds.
With 100 kilograms for 12 repetitions the estimate is 140.2 kilograms, from 140.0, 144.0, 135.4 and 141.5. The page warns here, because the set is longer than 10 repetitions.
Where the equations come from
The Epley equation did not come from a study. A 2026 review says that it was taken from a poundage chart in a University of Nebraska training manual of 1985. The Brzycki equation of 1993 appeared in a practitioner article, and the Mayhew equation of 1992 was fitted to the bench press of 435 college students. The same review says that such equations typically rest on small samples of young, trained males who bench pressed.
That history is why the answer shows four estimates and not one. Treat the spread between them as the size of the doubt.
What it leaves out
The estimate is for planning. It is not a test of your strength and it is not training advice. It does not know your lift, your technique or your fatigue, and the number of repetitions that a percentage allows differs between people.
Sources
- Nuzzo et al., Maximal Number of Repetitions at Percentages of the One Repetition Maximum: A Meta-Regression and Moderator Analysis of Sex, Age, Training Status, and Exercise (Sports Medicine, 2024), read on 2026-11-01.
- Marzagao, A Weight-Dependent 1RM Prediction Equation Optimized on 303,494 Near-Failure Sets Across 388 Exercises (preprint, 2026): its review of the classical equations, read on 2026-11-01.
Questions
How do you estimate a one rep max?
An equation turns the weight and the repetitions of a set into an estimate of one lift. The Epley equation multiplies the weight by 1 plus the repetitions over 30, so 185 pounds for 5 repetitions gives 215.8 pounds.
Which one rep max formula is the most accurate?
No equation is known to win everywhere. A 2026 review of the studies, which has not been peer reviewed, reports that accuracy depends on the lift and falls above about 10 repetitions. The page shows four equations and their average so that you can see how far they differ.
How many repetitions can I do at a percentage of my one rep max?
It differs from person to person and from lift to lift. A 2024 analysis of 952 tests on 7,289 people found that the repetitions fall as the percentage rises, and that the leg press allows more than the bench press. Treat the percentages as a starting point.
Why does the calculator stop at 15 repetitions?
The review above reports that the equations are less reliable beyond about 10 repetitions. The calculator warns above 10 and stops at 15. For one repetition, the weight itself is your one rep max.
How do the four equations differ?
Epley adds a thirtieth of the weight for each repetition, and Brzycki scales the weight by 36 over 37 minus the repetitions. Mayhew and Wathen use an exponential curve. For 185 pounds and 5 repetitions they give 215.8, 208.1, 220.2 and 215.7 pounds.
Published . Updated .