One Rep Max (1RM) Calculator

About One Rep Max (1RM) Calculator

The one-repetition maximum (1RM) is the maximum amount of weight that a person can possibly lift for one repetition. It's a common measurement used in weight training to assess strength and to determine the appropriate amount of weight to use in training programs.

How to Calculate One Rep Max

Since testing your 1RM can be dangerous if done improperly, several formulas have been developed to estimate your 1RM based on the amount of weight you can lift for multiple repetitions. This calculator uses six different formulas:

1. Brzycki (1993): 1RM = w × (36 / (37 - r))
2. Epley (1985): 1RM = w × (1 + 0.0333 × r)
3. Lombardi (1989): 1RM = w × r^0.1
4. Mayhew et al. (1992): 1RM = (100 × w) / (52.2 + (41.9 × e^(-0.055 × r)))
5. O'Conner et al. (1989): 1RM = w × (1 + 0.025 × r)
6. Wathan (1994): 1RM = (100 × w) / (48.8 + (53.8 × e^(-0.075 × r)))

Where:
w = weight lifted
r = number of repetitions performed
e = base of natural logarithm (~2.71828)

Why 1RM Matters

Knowing your 1RM is useful for:

• Designing personalized training programs
• Tracking strength progress over time
• Setting appropriate weight percentages for different training goals (endurance, hypertrophy, strength)
• Comparing strength levels between different exercises or with other lifters

Safety Considerations

While estimating your 1RM with formulas is safer than actually testing it, keep in mind:

• Formulas become less accurate with higher rep counts (above 10 reps)
• Different formulas may work better for different individuals or exercises
• Always use proper form and have a spotter when attempting heavy lifts
• Gradually work up to heavy weights with proper warm-up sets