One rep max calculator
Estimate your one rep max from a set you have actually done. Both the Epley and Brzycki formulas are shown, along with a training percentage table built from the result.
Your set
Estimated one rep max
Both formulas are most reliable at 10 reps or fewer.
weight × (1 + reps ÷ 30)
Brzycki
weight × 36 ÷ (37 − reps)
Training percentages
Most programmes prescribe load as a percentage of your one rep max. This table is built from the average above and updates with it.
| 100% | 115 kg |
|---|---|
| 95% | 109 kg |
| 90% | 103 kg |
| 85% | 97 kg |
| 80% | 92 kg |
| 75% | 86 kg |
| 70% | 80 kg |
| 65% | 74 kg |
| 60% | 69 kg |
| 55% | 63 kg |
| 50% | 57 kg |
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How the estimate works
A one rep max is the heaviest weight you can lift once with good technique. Testing one directly is fatiguing and carries more risk than most people need to take, so it is usually estimated from a heavier set of several reps instead.
Epley 1RM = weight × (1 + reps ÷ 30)
Brzycki 1RM = weight × 36 ÷ (37 − reps)
Both are long-standing estimates rather than measurements, and they disagree slightly by design: Epley tends to read a little higher as reps climb, Brzycki a little lower. Showing both, and their average, is more honest than presenting one number as fact.
At a single rep the two agree exactly, because at that point there is nothing to estimate.
Where the estimate breaks down
- Above about 10 reps. Accuracy falls away quickly, because high-rep sets are limited as much by conditioning as by strength.
- Sets not taken near failure. The formulas assume the set was genuinely hard. Reps left in reserve translate directly into an underestimate.
- Technical lifts. On the snatch and clean, technique fails before the muscle does, so a rep-based estimate means little.
- Beginners. Early strength gains come largely from coordination, so an estimate can be out of date within a fortnight.
Using percentages sensibly
Percentages are a starting point for the day, not a contract. Sleep, stress and food all move what you can lift, which is why Phasebuilt plans prescribe reps in reserve alongside load: if the prescribed weight moves badly on the day, the weight is wrong, not you. Re-estimate every four to six weeks rather than chasing a number that is already stale.
For how to add load over time without stalling, see progressive overload.
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