One Rep Max Calculator
Calculate your true 1RM maximum lift weight across Brzycki and Epley equations with full percentage rep ranges for powerlifting programming.
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How 1RM Formulas Work
Attempting a true maximal 1RM lift in training carries significant injury risk to tendons and central nervous system fatigue. Sub-maximal testing formulas safely predict your 1RM from 3 to 8 rep sets:
Epley Formula
1RM = Weight × (1 + 0.0333 × Reps)
Brzycki Formula
1RM = Weight × [36 / (37 - Reps)]
Why Formula Accuracy Drops Over 10 Reps
Sets of 10 or more reps test aerobic muscular endurance and lactic acid buffering rather than pure myofibrillar force production. For highest mathematical precision, use a heavy set of 3 to 5 reps taken to 1 rep in reserve (RIR 1).
Frequently Asked Questions
Which 1RM formula is most accurate?
The Epley and Brzycki formulas are the gold standards in exercise science literature. Epley tends to be slightly more accurate for squats and deadlifts, while Brzycki is preferred for upper body presses.
What is a good training percentage for building muscle (hypertrophy)?
Hypertrophy is optimized working with 70% to 80% of your 1RM for sets of 6 to 12 repetitions taken near muscular failure.
How often should you retest your 1RM?
Most strength athletes recalculate their 1RM at the end of a 4-to-8 week training block, rather than testing maximal singles weekly.