One Rep Max Calculator

Estimate your one rep max (1RM) using multiple proven formulas. Get training percentages, rep estimates, and comprehensive strength analysis.

Your Lift

Enter the weight you lifted

Range: 1-30 reps

Enter the weight you lifted and the number of reps performed, then click Calculate to see your estimated one rep max with detailed analysis.

Complete User Guide

What is One Rep Max (1RM)?

One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise. It's a fundamental metric in strength training used to:

  • Determine training intensities (percentages of 1RM)
  • Track strength progress over time
  • Design periodized training programs
  • Compare strength levels

Since testing your true 1RM can be dangerous and requires proper preparation, calculators use formulas to estimate it based on submaximal lifts (lighter weights for multiple reps).

1RM Calculation Formulas

Brzycki Formula

1RM = Weight / (1.0278 - 0.0278 × Reps)

Most popular formula. Generally accurate for 1-10 reps.

Epley Formula

1RM = Weight × (1 + Reps/30)

Simple and widely used. Good for moderate rep ranges.

Lombardi Formula

1RM = Weight × Reps^0.10

Power-based formula. Works well for higher rep ranges.

O'Conner Formula

1RM = Weight × (1 + Reps/40)

Conservative estimate. Good for beginners.

Mayhew Formula

1RM = (Weight × 100) / (52.2 + 41.9 × e^(-0.055 × Reps))

Exponential formula. Accurate across wide rep ranges.

Wathan Formula

1RM = (Weight × 100) / (48.8 + 53.8 × e^(-0.075 × Reps))

Another exponential formula. Good alternative to Mayhew.

The calculator uses the average of all formulas for the most accurate estimate. Different formulas may give slightly different results, which is why using multiple formulas and averaging provides the best estimate.

How to Use This Calculator

  1. Select your unit system (Metric or Imperial)
  2. Enter the weight you successfully lifted (use a weight you can lift for the specified reps with good form)
  3. Enter the number of reps you performed (1-30 reps)
  4. Click 'Calculate 1RM' to see your estimated one rep max
  5. Review the training percentages and rep estimates for program design
  6. Use the results to plan your training intensities

Understanding Your Results

Estimated 1RM

The average of all formulas. This is your best estimate of your true one rep max. Use this as your reference point for training.

Training Percentages

The weight you should lift at different percentages of your 1RM. Common training zones: 50-60% (endurance), 70-80% (hypertrophy), 85-95% (strength), 100% (maximal strength).

Estimated Max Reps

Approximate number of reps you could perform at different percentages of your 1RM. Useful for rep-based training programs.

Formula Comparison

Shows how different formulas estimate your 1RM. The range gives you an idea of the uncertainty in the estimate.

Training Zones by Percentage

50-60%: Endurance Zone

High volume, low intensity. Builds muscular endurance and work capacity. 12-20+ reps.

70-80%: Hypertrophy Zone

Moderate volume and intensity. Optimal for muscle growth. 8-12 reps.

85-95%: Strength Zone

High intensity, lower volume. Builds maximal strength. 1-5 reps.

95-100%: Maximal Strength

Peak intensity. Used sparingly for testing or peaking. 1 rep only.

Important Notes

  • 1RM estimates are most accurate when using 1-10 reps. Accuracy decreases with higher rep counts.
  • Always use a weight you can lift with proper form. Poor form leads to inaccurate estimates and injury risk.
  • 1RM varies by exercise. Bench press, squat, and deadlift will have different 1RMs. Calculate separately for each.
  • If you want to test your true 1RM, do so with proper warm-up, spotters, and safety equipment. Consider working with a qualified strength coach.

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