By Zencalcy Editorial TeamLast reviewed About us
Estimate your one rep max, the heaviest weight you could lift for a single clean repetition, from a set you have already performed. Enter the weight and the reps you completed, and the calculator applies the Epley or Brzycki formula, then lists training weights as a share of the result. Treat the figure as a good estimate rather than a tested lift.
Estimate your one rep max from a set you already did.
Epley: 1RM = weight × (1 + reps ÷ 30) Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Both formulas are most reliable at one to ten reps, where the underlying rep max data is dense. As reps rise the estimate drifts, and Brzycki is undefined at 37 reps or more, so the reps are capped at twelve here.
| Symbol | Meaning |
|---|---|
| weight | The load you lifted in the working set, in kilograms. |
| reps | How many reps you completed with that weight, 1 to 12. |
| 1RM | The estimated one rep max, the heaviest weight for a single rep. |
Lifting 100 kg for 5 reps gives an Epley estimate of 100 × (1 + 5 ÷ 30) = 116.7 kg and a Brzycki estimate of 100 × 36 ÷ 32 = 112.5 kg. The two sit close together, which is typical of the five rep range, while a set of ten would separate them more.
A one rep max estimate turns a set you can actually perform into the heaviest weight you could lift once. The Epley formula computes it as the weight lifted times one plus the reps divided by thirty, so eighty kilograms for eight reps estimates a max near 101.3 kilograms. The Brzycki formula instead multiplies the weight by thirty six and divides by thirty seven minus the reps, giving about 99.9 kilograms for the same set.
Both are regressions fitted to rep max data, and they agree closely at low repetitions. They separate as reps climb, because Brzycki divides by a term that shrinks toward zero as the rep count approaches thirty seven, so it inflates the estimate faster than Epley at very high reps.
Neither equation can know your training history, muscle fibre mix, or technique, so an estimate drawn from a high rep set carries more error than one taken from a low rep set.
The estimates are most trustworthy with sets of about three to six reps, where the underlying data is densest and fatigue has not yet distorted the relationship between load and repetitions.
Because each formula models a slightly different athlete, many calculators average the two or let you pick, and a difference of a few percent between them is normal rather than a sign of error. Test the estimate with a single near maximal lift only when it is safe and supervised.
Continue with the Plate Calculator, 5/3/1 Calculator, or the Bench Press Calculator — or browse more weightlifting tools and all sports calculators.
Neither is exact. Epley tends to read a little higher and Brzycki a little lower. At low reps they agree closely, so averaging the two gives a balanced figure.
Every result is computed locally in your browser from the formulas shown above. Nothing you type is uploaded, logged, or stored, and no account is required.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Content updated: September 2026