A one-rep max is the heaviest weight you can lift once with good form. Testing it properly takes a warm-up pyramid, a spotter and a day of fresh legs, so most people estimate it instead from a set they have already done. That is what this calculator does: you give a weight and the number of reps you completed, and it works backwards to the single.
How it is calculated
- Epley: 1RM = weight × (1 + reps ÷ 30).
- Brzycki: 1RM = weight × 36 ÷ (37 − reps).
- Lander: 1RM = weight × 100 ÷ (101.3 − 2.67123 × reps).
- Lombardi: 1RM = weight × reps0.10.
- The headline number is the average of Epley and Brzycki, the two most widely used. All four are listed so you can see how much they disagree.
Example
You bench 100 kg for 5 reps. Epley gives 100 × (1 + 5/30) = 116.7 kg. Brzycki gives 100 × 36/32 = 112.5 kg. The average is 114.6 kg, so a single at 115 kg is a realistic target and 110 kg should be comfortable.
How accurate is it
Correlations between predicted and actual maxes are high, above 0.95 in published tests, but the absolute error matters more than the correlation. Accuracy is best from three to six reps and falls away as reps rise. Studies also found the equations systematically underestimate the deadlift, so treat a deadlift estimate as a floor rather than a ceiling. Two things skew the result more than the choice of formula: stopping short of failure, which makes the estimate too low, and sloppy form, which makes it too high.
Why the percentage table matters
Lean mass sets a rough ceiling on what a drug-free lifter can move; the FFMI calculator puts a number on that side of it. Programmes are written in percentages of 1RM: five sets of three at 85%, or a back-off set at 70%. Once you have an estimate, the table under the result converts it to actual plate weights. The rep figures next to each percentage are population averages from a 2024 meta-regression covering more than a hundred studies; your own numbers can differ by several reps, and differ more on leg exercises than on upper-body ones.
Frequently asked questions
How do I calculate my one-rep max?
Take a set you have done close to failure and apply Epley (weight × (1 + reps/30)) or Brzycki (weight × 36/(37 − reps)). For 100 kg × 5 reps both land near 113–117 kg. The calculator above runs four formulas and averages the two main ones.
How many reps give the most accurate estimate?
Three to six. One rep needs no estimate, and above ten the formulas start to disagree by a lot because endurance rather than maximal strength limits the set.
Which formula is best, Epley or Brzycki?
They agree closely at low reps and diverge as reps rise, with Epley returning the higher number. Neither is reliably better across all lifts, which is why the headline figure here is their average.
Should I actually test my one-rep max?
Only if you are experienced, warmed up, and have a spotter or safety bars. An estimate is enough to set working weights for a programme, and it carries none of the injury risk of a true max attempt.
Why is my deadlift estimate lower than what I can lift?
Published comparisons found that these equations underestimate the deadlift specifically, while being closer on the bench press and squat. If your deadlift single beats the estimate, that is expected.
Sources
- Mayhew JL et al. Accuracy of prediction equations for determining one repetition maximum bench press in women before and after resistance training. J Strength Cond Res, 2008
- Nuzzo JL et al. Maximal Number of Repetitions at Percentages of the One Repetition Maximum: A Meta-Regression and Moderator Analysis. Sports Med, 2024 — source of the reps-per-percentage figures
By Calcelate Team. Formula from the sources above.
- 2026-09-15 · Formula and texts checked