One Rep Max Calculator
Your estimated maximum from a set you have already done, with the disagreement between formulas shown rather than hidden.
In short
One rep max is estimated from a submaximal set rather than tested directly. The Epley formula, weight multiplied by one plus reps divided by thirty, is the most common. Accuracy falls sharply above about eight reps, so estimate from sets of three to six for the most reliable figure.
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Why estimate rather than test
A true one rep max attempt is a maximal effort with maximal technical demand and no room left for error. It is fatiguing enough to disrupt the rest of the week, and the moment form breaks down under a maximum load is the moment people get injured.
An estimate from a hard set of five carries almost no risk and is accurate enough for the thing you actually need it for, which is choosing weights for your programme. Competitive lifters test because the number is the point. For everyone else it is an input, not an outcome.
The formulas
Epley 1RM = w x (1 + r / 30)
Brzycki 1RM = w x 36 / (37 - r)
Lombardi 1RM = w x r ^ 0.10
O'Conner 1RM = w x (1 + r / 40)At five reps they agree closely. At twelve they can differ by more than 5%, which on a heavy lift is a meaningful gap. The honest answer is the range rather than any single figure, which is why all four are shown.
Every one of them assumes the set was taken close to failure. An estimate from a comfortable set understates your max, and one from a set with sloppy final reps overstates it.
Reps to percentage
| Reps to failure | Roughly % of max |
|---|---|
| 1 | 100% |
| 2 | 95% |
| 3 | 93% |
| 5 | 87% |
| 8 | 80% |
| 10 | 75% |
| 12 | 70% |
| 15 | 65% |
These are population averages and individuals vary considerably. Some people can grind out twelve reps at 80% while others manage seven, largely down to muscle fibre composition. After a few months of training you will know which you are, and your own observed numbers beat the table.
Using percentages to programme
- 90 to 100% for 1 to 3 reps. Maximal strength. Demanding to recover from, so used sparingly.
- 80 to 90% for 3 to 6 reps. The main strength range for most people.
- 70 to 80% for 8 to 12 reps. Where most hypertrophy work sits.
- 60 to 70% for 12 to 20 reps. Endurance and technique volume.
- Under 60% for warm ups, speed work and movement practice.
A common error is treating a calculated max as a fixed property. It moves with sleep, food, stress and where you are in a training block, sometimes by 10% week to week. Many programmes deliberately use a "training max" of about 90% of the estimate to build that variation in.
Where this is less reliable
Technically complex lifts. Snatch and clean and jerk are limited by speed and positioning rather than raw force, so rep-based estimates do not transfer.
Isolation exercises. Curls and lateral raises fatigue differently and the formulas were not fitted to them.
Bodyweight movements. Pull ups and dips need your bodyweight added before the arithmetic makes sense.
Beginners. In the first few months, technique improves faster than strength, so an estimate is out of date almost immediately. That is a good problem.
An estimate for programming, not a target to attempt. Warm up properly, use a spotter or safety bars for anything heavy, and stop a set when form breaks rather than when the count says so.
Frequently asked questions
How is one rep max estimated?
From a set you have actually completed. The Epley formula, weight multiplied by one plus reps divided by thirty, is the most widely used. Four formulas are shown here because they disagree by a few percent and the spread is useful information in itself.
How many reps should I use for the estimate?
Three to six. Accuracy falls sharply above about eight because endurance starts to matter more than maximum strength, and the formulas were fitted to lower rep ranges. An estimate from a set of fifteen is close to a guess.
Should I actually test my max?
Rarely, and not without experience and a spotter. A true max attempt is technically demanding, fatiguing enough to disrupt a week of training, and the point at which form breaks down is the point at which people get hurt. An estimate from a hard set of five is safer and good enough for programming.
Why do the four formulas disagree?
Because they were fitted to different populations and lifts. Epley and Brzycki are close at low reps and diverge above ten. Treat the range as the honest answer rather than picking whichever number is highest.
Does this work for every lift?
Better for some than others. It is reasonably reliable for squats, deadlifts and presses, where the limiting factor is force production. It is less useful for lifts where technique or stability dominates, and unreliable for anything explosive like an olympic lift.