One-rep max calculator
Enter the weight and reps from a hard set and get an estimated one-rep max, plus the working weights for every percentage you are likely to program.
| % of 1RM | Weight (kg) | Typical reps |
|---|---|---|
| 100% | 115.5 | 1 |
| 95% | 109.8 | 2 |
| 90% | 104 | 4 |
| 85% | 98.2 | 6 |
| 80% | 92.4 | 8 |
| 75% | 86.7 | 10 |
| 70% | 80.9 | 12 |
| 65% | 75.1 | 15 |
How the calculator works
A one-rep max estimate predicts the heaviest single you could lift from a set of several reps. This calculator runs three standard formulas and averages them:
- Epley: weight × (1 + reps ÷ 30)
- Brzycki: weight × 36 ÷ (37 − reps)
- Lombardi: weight × reps0.10
A single rep returns the weight itself. The percentage chart then scales your estimated max to give a working weight for each rep target.
How accurate is it?
Estimates are most reliable from sets of about three to eight hard reps. Above ten reps, endurance, grip and breathing start to matter as much as strength, and the formulas drift. The calculator stops at 12 reps for that reason.
Treat the result as a planning number, not a test result. Technique, depth, bar speed and how close to failure the set really was all change it. Use the same lift standard each time so your estimates stay comparable.
Using your estimated max
Pick a rep target, find the matching percentage in the chart, and load that weight. Heavy triples sit near 90%, a strength set of five near 85%, and sets of eight to twelve between 70% and 80%.
The more useful habit is repeating the estimate. If the same lift estimates higher month after month, you are getting stronger, even if you never test a true max.
Questions
Which 1RM formula is most accurate?
None wins everywhere. Epley and Brzycki agree closely under about eight reps, and Lombardi runs a little higher. The calculator averages the three, which smooths out each formula’s quirks.
Should I test my true one-rep max?
Rarely. A true max is tiring, risky without spotters, and varies with how you slept. A hard set of three to eight reps, converted to an estimate, tracks strength just as well and costs far less recovery.
Why does the estimate change between lifts?
Rep endurance differs by exercise and by person. Many lifters get more reps at a given percentage on leg press than on bench, so the same formula over- or under-shoots depending on the lift.
Track your estimate every session.
Fortis logs your sets and plots your estimated 1RM per lift over time, so you see strength trends without testing a max.
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