One Rep Max (1RM) Calculator
Estimate your one-rep max and training percentages from a set's weight and reps.
| % of 1RM | Load (kg) |
|---|---|
| 95% | 108.9 |
| 90% | 103.1 |
| 85% | 97.4 |
| 80% | 91.7 |
| 75% | 85.9 |
| 70% | 80.2 |
| 65% | 74.5 |
| 60% | 68.8 |
| 55% | 63.0 |
| 50% | 57.3 |
This one-rep max calculator estimates the heaviest weight you could lift for a single repetition of an exercise, without you having to attempt a risky maximal lift. Enter a weight you lifted and how many reps you managed, and it predicts your 1RM by averaging two well-known formulas, Epley and Brzycki.
Your estimated 1RM is a useful anchor for programming: most strength routines prescribe working weights as a percentage of it. The calculator prints a full percentage table so you can quickly read off loads for hypertrophy, strength and power work. Estimates are most accurate for rep counts under about 10 — the further you go beyond that, the more the prediction drifts.
How to use it
- 1Choose your unit, kilograms or pounds.
- 2Enter the weight you lifted for the set.
- 3Enter how many clean repetitions you completed.
- 4Read your estimated 1RM and use the percentage table to set training loads.
Frequently asked questions
How is the one-rep max estimated?+
The calculator uses two formulas: Epley, which is weight × (1 + reps ÷ 30), and Brzycki, which is weight × 36 ÷ (37 − reps). It averages the two for a balanced estimate. Brzycki is only defined below 37 reps, so very high rep counts fall back to Epley alone.
How many reps give the most accurate estimate?+
Sets of around 3 to 10 reps give the most reliable 1RM estimates. As reps climb higher, fatigue, technique and endurance start to dominate, so the prediction becomes less precise. For the best read, use a challenging set that you take close to failure.
What is the percentage table for?+
Strength programs often prescribe loads as a percentage of your 1RM — for example 80% for strength work or 65% for higher-rep hypertrophy. The table converts your estimated max into concrete working weights so you can load the bar without recalculating each set.
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