One Rep Max (1RM) Calculator

Estimate your maximum strength for one repetition.

Usually most accurate between 2-10 reps.

Enter weight lifted and reps performed.

1RM estimations are most reliable for lower rep ranges (typically < 10-12). Accuracy varies by formula, individual, and exercise type. Use as a guide, not a definitive maximum.

Estimating Your One-Rep Max (1RM)

Your One-Repetition Maximum (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. Knowing your estimated 1RM is valuable for strength training program design, as many programs base lifting percentages on this number. Directly testing your true 1RM can be risky and requires proper technique and spotting. Therefore, calculators using formulas based on the weight you can lift for multiple repetitions are commonly used to estimate it.

How to Use

  1. Enter the Weight you successfully lifted. Select the unit (lbs or kg).
  2. Enter the number of Repetitions you completed with that weight (typically between 2 and 12 for best estimation).
  3. Choose a Formula (Epley and Brzycki are very common, others offer variations).
  4. Click "Calculate 1RM".

The results will show your estimated 1RM in both lbs and kg, and often include percentages of that 1RM (e.g., 90%, 80%, 70%) which are useful for programming subsequent workouts.

Common 1RM Formulas

Most formulas work by relating the weight lifted (w) and repetitions performed (r) to the theoretical 1RM. Examples:

  • Epley (1985): 1RM = w * (1 + r / 30)
  • Brzycki (1993): 1RM = w / (1.0278 - 0.0278 * r)
  • Lombardi: 1RM = w * r0.10
  • O'Conner et al.: 1RM = w * (1 + 0.025 * r)
  • *(Other formulas like Lander, Mayhew, Wathan exist with different coefficients or structures)*

Accuracy and Considerations

  • Rep Range:** Formulas are generally most accurate for reps between 2 and 10-12. Estimations based on very high reps (15+) become less reliable.
  • Formula Choice:** Different formulas yield slightly different results. Epley and Brzycki are widely used. No single formula is perfect for everyone or every exercise.
  • Exercise Type:** Accuracy can vary depending on the exercise (e.g., estimations might differ between bench press and squats).
  • Individual Factors:** Training experience, muscle fiber type, and technique influence actual 1RM.

Use the estimated 1RM as a guideline for setting training weights. Always prioritize proper form and safety. If attempting a true 1RM, do so under supervision with appropriate warm-ups and spotting.