One Rep Max (1RM) Calculator: estimated maximum strength

This calculator estimates your one rep max (1RM), the maximum weight you can lift for a single repetition, based on the weight you can lift for multiple repetitions using Epley's formula.

Epley's 1RM formula

The most widely used formula is:

1RM = weight × (1 + reps / 30)

This formula is accurate for 2-12 rep ranges. Beyond 12 reps, the estimate loses precision.

Example 1: bench press

Problem: You can do 8 reps with 80 kg on bench press.

1. Calculation:
   • 1RM = 80 × (1 + 8/30) = 80 × 1.267 ≈ 101.3 kg.

Answer: Your estimated 1RM is approximately 101.3 kg.

Example 2: squat

Problem: You can do 5 reps with 120 kg on squat.

1. Calculation:
   • 1RM = 120 × (1 + 5/30) = 120 × 1.167 ≈ 140 kg.

Answer: Your estimated 1RM is approximately 140 kg.

Common uses of 1RM

• Planning training loads based on 1RM percentages.
• Tracking strength progression without max testing.
• Comparing strength levels across different exercises.
• Setting realistic strength goals.
• Programming periodization and training cycles.
• Evaluating the effectiveness of strength programs.

Common mistakes with 1RM

• Using the formula with more than 12 reps (loses accuracy).
• Not considering that the formula is an estimate, not an exact measure.
• Attempting a real 1RM without proper warm-up or supervision.
• Not accounting that different exercises have different fatigue curves.

Pro tip

For training, use 1RM percentages: 60-70% for hypertrophy (8-12 reps), 75-85% for strength (4-6 reps), 90%+ for max strength (1-3 reps). Re-estimate your 1RM every 4-6 weeks.