One-Rep Max Calculator

Your one-rep max (1RM) is the most weight you could lift for a single repetition of a given exercise. It's the reference strength coaches and lifters use to program training — most structured plans prescribe loads as a percentage of 1RM (for example, 5 sets of 5 at 80%).

Estimating your 1RM from a set you've actually done is safer and more practical than repeatedly attempting true maxes. You lift a weight for a few hard reps, and the formula projects what you could manage for one. The fewer reps you use, the more accurate the estimate.

Treat the result as a well-grounded estimate, not a guarantee. Your real 1RM depends on the exercise, your technique on the day, and how close to failure your set actually was — so use it to guide training loads, then adjust based on how the weights feel.

Formulas. Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight ÷ (1.0278 − 0.0278 × reps). We report Epley as the primary estimate and Brzycki as a cross-check; at a single rep, both return the weight you lifted. Reps are capped at 15 because the equations lose validity beyond about 12.

Sources. The Epley formula (1985) and the Brzycki formula (1993) are two of the most widely used 1RM prediction equations in strength training.

Confidence. We label this moderate confidence: it's a reliable estimate for low-to-moderate rep sets, but accuracy drops as reps rise, and it varies by exercise and individual. Use it as a training guide, not a certified max.