1 Rep Max (1RM) Calculator

Why Calculate Your 1 Rep Max?

Your One Repetition Maximum (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise. It is the gold standard for measuring raw strength.

However, physically testing your true 1RM is incredibly taxing on the central nervous system and carries a high risk of injury, especially for beginners. By using a 1RM calculator, you can estimate your max based on a safer 3-rep or 5-rep max.

How is 1RM Calculated?

There is no perfect mathematical equation for the human body, but sports scientists have developed several highly accurate formulas. Our calculator averages the two most respected equations:

• The Epley Formula: 1RM = Weight × (1 + 0.0333 × Reps)
• The Brzycki Formula: 1RM = Weight × (36 / (37 - Reps))

Note: These formulas are highly accurate for sets of 1 to 5 reps. If you enter 15 reps, the calculation becomes less reliable because muscular endurance begins to override pure strength.

Using Training Percentages

Most professional strength programs (like Jim Wendler's 5/3/1) dictate your daily workouts as a percentage of your 1RM. For example:

• Power/Max Strength: 85% - 100% (1 - 5 reps)
• Hypertrophy (Muscle Size): 70% - 80% (8 - 12 reps)
• Endurance: < 65% (15+ reps)