One Rep Max Calculator
Calculate your 1RM and generate your training percentages safely.
Weight Lifted
Reps Performed
⚠️ Safety Disclaimer
This calculator provides an estimate of your one-rep max based on sports science formulas. It is not a substitute for professional coaching. Lifting maximal weights carries a high risk of injury. Always ensure you are properly warmed up, use correct form, and have a spotter present when attempting heavy lifts.
How is 1RM Calculated?
A One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition. Because testing your true 1RM is physically exhausting and carries injury risks, strength coaches use formulas to estimate it based on sub-maximal lifts (like lifting a lighter weight for 5 reps).
- The Formulas: This calculator averages the two most widely accepted sports science formulas: the Epley formula ($W \times (1 + R / 30)$) and the Brzycki formula ($W \times (36 / (37 - R))$).
- The Rep Limit: These formulas are most accurate when you input 10 reps or fewer. If you input a set of 15 or 20 reps, the formulas break down and become highly inaccurate.
- Why use percentages? Professional weightlifting programs (like 5/3/1 or Smolov) rarely require you to lift 100% of your max. Instead, they program working sets at specific percentages (e.g., 5 sets of 5 reps at 75% of your 1RM) to build volume and strength safely.