Transparent method
The formula
Worked example
Example inputs
How to interpret the result
The Epley formula and similar one-rep-max estimates lose accuracy as rep count climbs, because they're extrapolating a heavier single lift from a lighter, higher-rep set, and that extrapolation drifts further from reality the more reps separate the tested set from the actual single-rep effort being estimated.
Before you rely on it
What to check
Test with a set closer to failure and in a lower rep range for the most accurate estimate, rather than extrapolating from a high-rep, far-from-failure set.
The common error
Where people go wrong with one-rep max calculator
Trusting a one-rep-max estimate extrapolated from a set of 15 or more reps as precisely as one estimated from a near-failure set of 3 to 5. The formula's accuracy declines meaningfully as the tested set moves further from an actual single-rep effort.
Sensitivity evidence
How weight lifted changes the estimated one-rep max
| Weight lifted | Estimated one-rep max | 90% training weight |
|---|---|---|
| 108 | 136.8 | 123.1 |
| 122 | 154.5 | 139.1 |
| 135worked example | 171 | 153.9 |
| 149 | 188.7 | 169.9 |
| 162 | 205.2 | 184.7 |
Every input, tested
Which input moves the estimated one-rep max most
| Input | Tested from | To | Estimated one-rep max at each end | Swing |
|---|---|---|---|---|
| Weight lifted | 122 | 149 | 154.5 to 188.7 | 34.2 (20%) |
| Repetitions completed | 7 | 9 | 166.5 to 175.5 | 9 (5.3%) |
Two variables at once
Estimated one-rep max by weight lifted and repetitions completed
| Weight lifted \ Repetitions completed | 6 | 8 | 10 |
|---|---|---|---|
| 108 | 129.6 | 136.8 | 144 |
| 122 | 146.4 | 154.5 | 162.7 |
| 135 | 162 | 171 | 180 |
| 149 | 178.8 | 188.7 | 198.7 |
| 162 | 194.4 | 205.2 | 216 |
Step by step
The worked example, input by input
| Input | Value used | What it means |
|---|---|---|
| Weight lifted | 135 | Weight lifted for the set, in pounds. |
| Repetitions completed | 8 | Repetitions completed with good form. Most accurate under 12 reps. |
| Estimated one-rep max | 171 | |
| 90% training weight | 153.9 | |
Inputs, definitions and assumptions
Weight lifted
Weight lifted for the set, in pounds.
Repetitions completed
Repetitions completed with good form. Most accurate under 12 reps.
Where the inputs come from
Enter the weight you lifted and the number of repetitions you completed with good form, ideally in a set taken close to failure. The Epley formula multiplies the weight by one plus the reps divided by 30. Estimates are most accurate for sets of 2 to 10 repetitions and get less reliable above about 10. Use a set you actually performed, and only if you can lift safely: this tool estimates a maximum so you do not have to test it.
When the result stops applying
Formulas differ, and results vary by lift and by the person: lifts using many muscles predict better than isolation exercises. Fatigue, technique and rest change performance. A true one-rep max carries injury risk, so most lifters use estimates. The Epley formula tends to overestimate at high repetitions.
What to compare it with
Compare strength across bodyweights on the Wilks score calculator, and plan protein on the protein intake page. The calories burned and target heart rate pages cover cardio. Use a spotter or safety pins when lifting heavy.
People also ask
Frequently asked questions
How is one-rep max estimated?
Formulas such as Epley use the weight lifted and the repetitions completed to predict the heaviest single lift, and they are most accurate for sets of up to about ten reps.
Is it safe to test a true one-rep max?
It carries injury risk and requires a spotter and good technique. Most people can train effectively using estimated maxes.
What percentage of my max should I train at?
Strength work is often at 80% to 90%, muscle growth at about 65% to 80% and endurance at lighter loads with higher repetitions.