One rep max calculator
Put in a set you actually did. This gives you the estimated one-rep max both common formulas produce, and the percentages to program from.
Units do not matter — the output is in whatever you typed. Above about 12 reps both formulas drift badly, which is why the table stops there.
Percentage of 1RM by reps
This is the part worth bookmarking. To work at a given rep target, take your 1RM and multiply by the percentage on that row.
| Reps | Brzycki | Epley |
|---|---|---|
| 1 | 100.0% | 96.8% |
| 2 | 97.2% | 93.8% |
| 3 | 94.4% | 90.9% |
| 4 | 91.7% | 88.2% |
| 5 | 88.9% | 85.7% |
| 6 | 86.1% | 83.3% |
| 7 | 83.3% | 81.1% |
| 8 | 80.6% | 78.9% |
| 9 | 77.8% | 76.9% |
| 10 | 75.0% | 75.0% |
| 11 | 72.2% | 73.2% |
| 12 | 69.4% | 71.4% |
Epley reads 96.8% at one rep rather than 100%, which looks like an error and is not: the formula is fitted to multi-rep data and does not resolve exactly at a single. Brzycki does. Past six reps the two diverge, Brzycki lower and Epley higher. Neither is a measurement — both are estimates fitted to population data, and your own ratio drifts with training age and with the lift.
The formulas
Brzycki — 1RM = weight × 36 ÷ (37 − reps). GymHack uses
this one to build your muscle profile, because it is the more conservative of the two in
the 5–10 rep range where most working sets live.
Epley — 1RM = weight × (1 + reps ÷ 30). GymHack uses
this one to detect estimated-1RM personal records, where the higher reading is the safer
bet against false positives.
Using two formulas for two jobs is deliberate. A single formula that is right on average is wrong in both of the places it matters.
Estimating is not testing
Every number on this page is inferred from a submaximal set. If you want your actual one-rep max, you have to work up to it — and doing that safely means a protocol, not a hero single at the end of a session. GymHack has a guided 1RM test that walks the warm-up ramp and records the attempt, and it flags the estimate as stale after twelve weeks so you are not programming off a number from last spring.
Frequently asked
Which formula should I use?
Why does the table stop at 12 reps?
Does GymHack calculate this for me?
