🏋 One Rep Max Calculator
Estimate the most you could lift once, from a set you have actually done. Five published formulas are shown side by side, with the training percentages for every rep range underneath.
Estimating your one rep max without attempting one
A one rep max is the heaviest weight you can lift once with good form. Testing it is useful, taxing and occasionally risky, so most training programmes estimate it from a set you have already done. The estimate is close enough to program with, provided you understand what it is built on.
The five formulas
| Formula | Equation | Known for |
|---|---|---|
| Epley | w × (1 + r/30) | The most widely used; slightly high at high reps |
| Brzycki | w × 36 / (37 − r) | Accurate at low reps; breaks down above 10 |
| Lombardi | w × r0.10 | Conservative at moderate reps |
| O'Conner | w × (1 + 0.025r) | Simple and conservative |
| Wathan | 100w / (48.8 + 53.8e−0.075r) | Best fit in several validation studies |
The calculator runs all five and averages them, because no single formula is reliably best across all lifts and all lifters. The spread between them is itself informative: when they disagree by more than about 5%, the estimate is doing more extrapolating than you probably want.
Reps and accuracy
All of these are extrapolations from a curve fitted to population data, and the further you extrapolate the worse it gets. Below five reps the formulas are generally within 2% to 3% of a tested max. By ten reps the error widens considerably, and above twelve the result is a rough indication at best, because sets that long become limited by muscular endurance and conditioning rather than by maximal strength.
The estimate assumes the set was taken close to failure with consistent technique. A set of five with three reps left in reserve will understate your max substantially, which is why training logs increasingly record reps in reserve alongside the weight.
Percentages for programming
| % of 1RM | Reps usually possible | Trains mostly |
|---|---|---|
| 95–100% | 1–2 | Maximal strength, neural |
| 90–95% | 2–4 | Strength |
| 85–90% | 4–6 | Strength and some size |
| 75–85% | 6–10 | Hypertrophy |
| 65–75% | 10–15 | Hypertrophy and endurance |
| under 65% | 15+ | Muscular endurance, technique work |
These are averages and individual variation is large. Some lifters manage eight reps at 85% while others manage four, and the pattern tends to differ by lift: most people get more reps at a given percentage on leg press than on bench press.
Which lifts this works for
Best for compound barbell lifts with a stable groove: squat, bench press, deadlift, overhead press, row. Less reliable for isolation exercises, where technique breaks down differently near failure, and unreliable for bodyweight movements, where the load cannot be varied smoothly.
A worked example
A lifter does 100 kg for 5 clean reps on the bench press. Epley gives 116.7 kg, Brzycki 112.5, Lombardi 117.5, O'Conner 112.5 and Wathan 116.6. The average is 115.1 kg, with a 5 kg spread. Programming at 80% of that is 92 kg for sets of eight, and a single at 95% would be about 109 kg.
This page explains published formulas and population averages. It is general information, not medical advice. Talk to a doctor or a registered dietitian before changing how you eat or train.
Frequently Asked Questions (FAQs)
How accurate is an estimated 1RM?
Within about 2% to 5% of a tested max when calculated from a set of five or fewer reps taken close to failure. Accuracy falls as the rep count rises, and above ten reps the estimate should be treated as indicative only.
Should I actually test my one rep max?
Occasionally, if you compete or if your programme calls for it, and only with a spotter and after a proper warm-up. For most people, estimating from a set of three to five is safer, less fatiguing and accurate enough to programme from.
Why do the five formulas disagree?
Each was fitted to a different population and set of lifts. Brzycki is steeper at low reps, Epley flatter at high ones. Their disagreement is a reasonable proxy for the uncertainty in any single estimate, which is why averaging them is more useful than picking one.
Does the 1RM differ between exercises?
The percentages do. Lifts using large muscle groups with a stable position, such as the leg press, usually allow more reps at a given percentage than lifts with a longer range and more stabilisation, such as the bench press. Build your own table from your own logs if you train seriously.
How often should I recalculate?
Every four to six weeks, or whenever a working set feels clearly easier than the programme expects. Strength changes faster than most people update their numbers, so training percentages drift downward in effectiveness over a long block.
Is a 1RM useful if I only want muscle, not strength?
Yes, as a reference for choosing loads. Hypertrophy work typically sits at 65% to 85% of 1RM, and knowing the max is how you keep that range honest as you get stronger rather than training the same weight for months.