One Rep Max Calculator

Your one-rep maximum (1RM) is the most weight you can lift for a single repetition with good form. This calculator estimates it from a submaximal set using the Epley formula — the most widely used method in strength training research. Because performing true maximum attempts carries injury risk and requires a spotter, most lifters use a challenging multi-rep set as the input and let the formula project their 1RM. It also calculates common training percentage zones — 90%, 80%, 70%, and 60% — so you can structure your workouts around proven rep ranges for strength, hypertrophy, and muscular endurance without needing to test your absolute maximum. These percentage-based zones are the foundation of most evidence-backed programming approaches, from linear progression for beginners to periodisation models used by competitive powerlifters and Olympic weightlifters. Knowing your 1RM for the squat, bench press, and deadlift lets you load each training session with purpose and track long-term strength progress objectively.

Uses the Epley formula: 1RM = weight × (1 + reps ÷ 30). This is the most widely cited formula in strength training research and is accurate for most lifters performing sets in the 2–10 rep range. The formula assumes that each additional rep beyond one represents approximately a 3.33% reduction from true max effort. Once you have your estimated 1RM, the calculator breaks it into standard training percentage zones — 90%, 80%, 70%, and 60% — which correspond to the heavy single, strength, hypertrophy, and endurance rep ranges used in modern programming. Estimates become progressively less reliable above 10 reps.