1RM Formula Explanations

Our calculator uses four proven scientific formulas to estimate your one-rep max. Each has different strengths and optimal rep ranges for maximum accuracy.

Epley Formula

1RM = Weight × (1 + Reps/30)

Best for:

  • Moderate rep ranges (3-8 reps)
  • General strength training
  • Most common and widely used

Accuracy:

Very reliable for 3-8 reps. Tends to slightly overestimate at very low reps (1-2) and underestimate at higher reps (9-12).

Brzycki Formula

1RM = Weight × 36 / (37 - Reps)

Best for:

  • Lower rep ranges (1-6 reps)
  • Powerlifting movements
  • Maximum strength testing

Accuracy:

Most accurate for 1-6 reps. Becomes less reliable above 8 reps. Preferred by powerlifters for its accuracy at low rep ranges.

Lombardi Formula

1RM = Weight × Reps^0.10

Best for:

  • Single rep attempts
  • Elite level athletes
  • Validation of other formulas

Accuracy:

Most conservative estimate. Often underestimates true 1RM, especially for higher rep ranges. Good as a safety baseline.

O'Conner Formula

1RM = Weight × (1 + 0.025 × Reps)

Best for:

  • Higher rep ranges (6-12 reps)
  • Bodybuilding movements
  • Endurance-strength training

Accuracy:

More conservative than Epley. Works well for moderate to higher rep ranges. Often preferred for safety when working with novice lifters.

Quick Comparison

Formula Best Rep Range Tendency Use Case
Epley 3-8 reps Moderate estimate General training
Brzycki 1-6 reps Higher estimate Powerlifting
Lombardi 1-3 reps Conservative Safety baseline
O'Conner 6-12 reps Conservative Higher rep training

Important Considerations

  • • Rep Range Matters: All formulas become less accurate beyond 12 reps. For best results, test between 1-10 reps.
  • • Individual Variation: Your actual 1RM may differ based on training background, muscle fiber type, and lifting technique.
  • • Exercise Specificity: Formulas work best for compound movements (squat, bench, deadlift) and may be less accurate for isolation exercises.
  • • Safety First: These are estimates. Always warm up properly and consider having a spotter for maximum attempts.
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