Free 1-Rep Max Calculator

What is a 1-Rep Max Calculator?

A One-Repetition Maximum (1RM) calculator predicts the absolute maximum amount of weight you can lift for a single, full-range-of-motion repetition. Instead of physically attempting a dangerous maximum lift, you can lift a slightly lighter weight for multiple repetitions (e.g., 5 to 8 reps) and use our mathematical formula to extrapolate your maximum ceiling safely.

The Brzycki Formula

We utilize the industry-standard Matt Brzycki formula to calculate your results. Developed by a strength and conditioning coach, this formula calculates your 1RM incredibly accurately when your reps fall within the 1-10 range. The equation is: Weight × (36 / (37 - Reps)).

Why Use Percentages for Program Design?

Almost all professional powerlifting and bodybuilding programming (such as 5/3/1, Smolov, or standard linear periodization) requires you to know your 1RM. Training is then structured around percentages of this maximum:

• 85% - 100%: Pure strength and central nervous system adaptation (Powerlifting).
• 70% - 85%: Optimal zone for muscle hypertrophy (Bodybuilding).
• 50% - 70%: Muscular endurance and explosive speedwork.

Calculator Accuracy & Limitations

This calculator is most accurate when the reps performed are 10 or fewer. The higher the number of reps you log (e.g., 15+ reps), the less accurate the 1RM extrapolation becomes, because the physiological pathway shifts from anaerobic explosive strength to muscular endurance.