Determining your One Rep Max (1RM) is the gold standard for measuring raw strength, but physically testing it places massive stress on the central nervous system and increases injury risk. Our science-backed One Rep Max Calculator allows you to estimate your maximum lift with high precision without ever needing to attempt a dangerous 100% effort lift.

 This tool uses industry-standard formulas to translate your sub-maximal efforts (e.g., a set of 5 reps) into a highly accurate 1RM estimate, giving you the data you need to calculate training percentages for Bench Press, Squats, Deadlifts, Overhead Press, and other exercises.

1RM Calculator

Calculate your maximum strength potential

Choose the exercise you performed.
Enter the total weight loaded on the bar.
Enter the number of reps performed to failure.
"Automatic" uses the best scientific model for your rep range.
Accuracy Note: You entered more than 10 reps. Scientific accuracy decreases significantly for high-rep sets. For a true 1RM estimate, we recommend testing with a weight you can lift for 3-5 reps.
Estimated One Rep Max 0 Range: 0 - 0
Use these percentages for your workout programming.
% Weight Reps
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How to Use This Calculator

  1. Select Your Lift: Choose the specific exercise (Bench, Squat, Deadlift, etc.). While the math is similar, identifying the lift helps you track your specific records.
  2. Enter Your Data: Input the weight you lifted and the number of clean repetitions you performed. Note: The repetitions must be performed to “technical failure” – meaning you could not complete another rep with perfect form.
  3. Analyze the Results: Hit calculate. The tool will provide your estimated max, a likely accuracy range, and a complete Percentage Table to help you plan your future sets (e.g., 5×5 at 85%).

One Rep Max Calculator - Science Backed Tool

The Science: Understanding the Formulas

The physiology of muscle failure follows a predictable “Force-Velocity” curve. As the weight on the bar decreases, the number of repetitions a human can perform increases linearly. This calculator allows you to choose between the four most proven scientific models:

1. The Brzycki Formula

Developed by Matt Brzycki in the early 90s, this formula is widely considered the most accurate for low-repetition sets (fewer than 5 reps). It accounts for the fact that energy depletion is less linear near maximal loads.

Formula: 1RM = Weight × (36 / (37 - Reps))

2. The Epley Formula

Boyd Epley, the “Godfather of Strength and Conditioning” at the University of Nebraska, created this formula in 1985. It is slightly more aggressive than Brzycki and is historically accurate for sets in the 6–12 rep range, often used by bodybuilders or athletes doing volume work.

Formula: 1RM = Weight × (1 + (Reps / 30))

3. The Lombardi Formula

The Lombardi formula is distinct because it uses an exponential calculations rather than a linear one. It is often favored by advanced powerlifters because it accounts for the “grind” of heavy repetitions, though it can sometimes underestimate 1RM for beginners who lack neuromuscular efficiency.

Formula: 1RM = Weight × Reps^0.10

4. The O’Conner Formula

The O’Conner (or O’Conner-Coleman) formula is mathematically similar to Epley but uses a divisor of 40 instead of 30. This makes it more conservative. It is an excellent choice for intermediate lifters who want a safer, slightly lower estimate to base their training program on.

Formula: 1RM = Weight × (1 + (Reps / 40))

Recommended: The “Automatic” Hybrid Logic

Research indicates that no single formula is perfect for every scenario. If you leave the tool on “Automatic,” it uses a unique weighted logic to give you the best of all worlds:

  • If you perform 1-4 reps, the tool prioritizes the Brzycki formula for precision.
  • If you perform 5-10 reps, the tool averages Epley and Brzycki to smooth out statistical anomalies.
  • If you perform 10+ reps, it relies on Epley, as it handles endurance-based extrapolation better than exponential models.

Sources & Research

The logic used in this calculator is based on peer-reviewed strength and conditioning research:

  • Matt Brzycki (1993): Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance. View Research
  • Boyd Epley (1985): The Dynamic Strength Test. University of Nebraska. Epley is the founder of the NSCA (National Strength and Conditioning Association). About Boyd Epley
  • Lombardi, V. P. (1989): Beginning Weight Training. Dubuque, IA: Wm. C. Brown Publishers.
  • Journal of Sports Science & Medicine (2013): Validity of the Brzycki and Epley Equations for the Estimation of 1RM in the Bench Press. View Study on NCBI

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