One rep max calculator
Estimate your one rep max from a set you have actually done, with four published formulas compared — because they disagree, and the disagreement is the useful part.
Estimate your 1RM
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| Estimated 1RM (average) | — |
|---|---|
| Epley | — |
| Brzycki | — |
| Lombardi | — |
| O’Conner | — |
| Spread between formulas | — |
Why four formulas instead of one
Every 1RM calculator is running an equation fitted to a population, and the published equations disagree. Showing one of them and calling it "your one rep max" hides that. Shown together, the spread tells you how much to trust the number.
At three to five reps the four agree within a couple of kilos. At ten reps they can differ by ten or more, because how many reps someone can do at a given percentage of their max varies enormously between individuals — it reflects fibre type, training history and pain tolerance as much as strength. A powerlifter and a rower with identical maxes will produce very different rep counts at 80%.
The practical rule
Estimate from a set of five or fewer. Above eight reps, treat the output as a rough upper bound rather than a target. And take the set close to failure but not to it: an estimate from a set you stopped three reps early understates your max, which is the safer direction to be wrong in.
Training percentages
| Reps | Roughly this % of 1RM | Typically used for |
|---|---|---|
| 1 | 100% | Testing |
| 3 | 93% | Maximal strength |
| 5 | 87% | Strength |
| 8 | 80% | Strength and size |
| 10 | 75% | Size |
| 15 | 65% | Endurance |
These are conventions rather than physical constants, and the same caveat applies: your own rep capacity at a given percentage may sit well away from the table.
Safety
A calculated 1RM is a number on a screen. Do not load a bar to it and attempt a single. If you want to test a genuine max, do it with a spotter or in a rack with safety pins, after a progressive warm-up, on a day you feel good — and accept that an off day will produce a lower number that means nothing about your training.
Common questions
How do I calculate my one rep max?
Take a set you have genuinely completed and apply a formula. Epley multiplies the weight by (1 + reps ÷ 30); Brzycki uses weight × 36 ÷ (37 − reps). The tool above shows four and their average, because they disagree.
Which 1RM formula is most accurate?
None is reliably best. They agree closely below six reps and diverge sharply above eight. The most accurate approach is estimating from a heavy set of three to five rather than choosing between formulas.
Is it safe to test my actual one rep max?
It carries more risk than estimating. If you do test, use a spotter or safety pins, warm up progressively, and accept that fatigue and sleep move the number substantially day to day.
What percentage of my max should I train at?
Roughly 87% for sets of five, 80% for eights and 75% for tens. These are conventions; individual rep capacity at a given percentage varies a great deal.
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