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1RM Calculator
Estimate your one-rep max from any weight and rep count using the Epley formula
Strength
kg
reps
What This Calculator Measures
The one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition with proper form. It is the gold standard for measuring absolute strength and is used by coaches and athletes worldwide to program training loads.
How It Works
This calculator uses the **Epley formula**, one of the most widely validated 1RM prediction equations:
**1RM = Weight x (1 + Reps / 30)**
For example, if you bench press 100 kg for 5 reps, your estimated 1RM is 100 x (1 + 5/30) = **117 kg**.
The formula is most accurate when reps are between 1 and 10. Above 10 reps, predictions become less reliable because muscular endurance begins to influence the outcome more than raw strength.
| Percentage of 1RM | Typical Rep Range | Training Effect |
|---|---|---|
| 90-100% | 1-3 reps | Maximal strength |
| 75-85% | 4-8 reps | Strength and hypertrophy |
| 65-75% | 8-12 reps | Hypertrophy |
| 50-65% | 12-20 reps | Muscular endurance |
Limitations
•Accuracy decreases with higher rep counts (above 10 reps).
•The formula assumes reps are performed to or near failure. If you had 3 reps left in reserve, the result will underestimate your true 1RM.
•Different exercises may follow slightly different strength curves. The Epley formula works best for compound barbell movements like squat, bench press, and deadlift.
•Individual variation in muscle fiber composition means no formula is perfectly accurate for everyone. Use the estimate as a starting point and adjust based on experience.