1RM Calculator: Estimate Your One Rep Max
Calculate your estimated one rep max using Epley and Brzycki formulas. Enter your weight and reps to find your 1RM instantly.
The single repetition maximum weight (1RM) counter estimates the maximum weight you can lift in a single repetition, based on the lighter set you have already performed. Enter your weight and number of reps below, and the calculator will return an estimated 1RM using two validated formulas.
How it works
Two formulas govern the estimation of 1RM. Both take as input the weight and the number of repetitions and return the predicted maximum.
Epley's formula: 1RM = weight x (1 + repetitions/30).
Brzyck's formula: 1RM = weight x (36 / (37 - repetitions))
Below 5 repetitions, the formulas produce almost identical results. Above 10 repetitions, they diverge. Neither is reliably accurate above 12 repetitions because high repetition sets test muscle endurance more than maximal strength.
Which formula to use
Epley generally predicts slightly higher results with moderate repetition rates (6-10). Brzycki is more conservative. Most coaches use Epley by default because it more closely matches the maximum power observed by trained lifters.
If your programming is based on your estimated max, use a lower number. If you decide whether to attempt a PR, use the higher one - with caution.
Why do estimated and actual 1RM differ?
Your true maximum knowledge depends on factors that no formula takes into account:
- Technique at maximum load. A set of five sets does not test your ability to grind through a slow, ugly single set.
- Neural readiness. Peak performance is a skill. Lifters who rarely lift heavy often underperform their estimated maximum weight.
- Fatigue from previous sets. If your pitching set came after 4 warm-up sets and 2 working sets, your actual maximum weight on a new attempt would be higher.
- Psychological factors. Heavy weight feels different. Some lifters slump, others rise to it.
A 1RM estimated for programming is more useful than a tested one. Testing the actual max is tiring, carries a risk of injury, and only tells you what you could do that day.
When to use the 1RM calculator?
- Setting training weights. In most percentage-based programs, loads are prescribed as fractions of 1RM. Estimate it and then calculate your workload.
- Tracking your progress. If your estimated 1RM increases over the weeks at the same repetition interval, you're getting stronger - no need to test.
- Compare lifts. Want to know if your squat or deadlift is proportionally stronger? Estimated 1RMs make the comparison even.
When not to use it
Don't enter sets of more than 15 reps and wait for a meaningful number. Don't use machine exercises - the formulas have been validated with compound movements of the weight bearing joint. And don't treat the result as gospel. It is a useful estimate, not a guarantee.
Quick reference
| Repetitions performed | Estimated % of 1RM |
|---|---|
| 1 | 100% |
| 2 | 95% |
| 3 | 93% |
| 5 | 87% |
| 8 | 80% |
| 10 | 75% |
| 12 | 70% |
These percentages are averages. Your individual rep-max curve depends on muscle fiber composition, training history and lifting target. Deadlifts generally allow for fewer reps at a given percentage than squats. Push-ups fall somewhere in between.
Use the calculator above to get your own number and then apply it to your program.