Why Calculate Instead of Test?
Testing a true 1-Rep Max (1RM) places massive stress on your joints, requires a reliable spotter (often two), and carries a significant risk of injury if form breaks down.
Science says: Calculating your max from a heavy 3-Rep or 5-Rep set is estimated to be 95% accurate to a true max, with a fraction of the injury risk.
Epley vs. Brzycki Formulas
The Epley Formula
The industry standard since 1985. It is generally the "go-to" for standard hypertrophy rep ranges (6-12 reps).
Weight × (1 + Reps/30)The Brzycki Formula
Slightly more conservative. Many powerlifters prefer this for lower rep ranges (tests < 5 reps) as it tends to be less aggressive.
Weight × (36 / (37 - Reps))How to Use Your Data
Strength Training
Train at 85-95% of your 1RM. Focus on low reps (1-5) with long rest periods. This builds raw force production.
Hypertrophy (Muscle Size)
Train at 70-85% of your 1RM. Focus on moderate reps (6-12). This optimizes metabolic stress and volume for growth.
Endurance
Train at less than 65% of your 1RM. Focus on high reps (15+). This builds fatigue resistance.
Frequently Asked Questions
How accurate is this calculator?
Does this work for all exercises?
What is a good 1RM for my age?
Tools & Data Verified by the EverydayCalculators Medical Research Team.
Last updated: January 2026.