Last updated: March 2026
What Is a 1RM Calculator?
A 1RM (one-rep max) calculator estimates the maximum weight you can lift for a single repetition based on a sub-maximal set. Enter the weight you lifted and how many reps you completed, and the calculator uses established formulas (Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner, Wathan) to predict your true max.
Frequently Asked Questions
What is a 1RM?
Your one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition with proper form. It's used to program training percentages and track strength progress.
Which formula is most accurate?
The Epley formula is the most widely used and generally accurate for reps under 10. The Brzycki formula is also very popular. The tool shows results from 7 formulas so you can compare.
How many reps should I use for accuracy?
Use 2-10 reps for the most accurate estimate. Predictions from sets of 15+ reps become less reliable.
Should I actually attempt my 1RM?
Testing a true 1RM carries injury risk, especially for beginners. Using a calculator with a moderate-rep set is safer and gives a good estimate for programming purposes.
How do I use 1RM percentages?
Typical training zones: 90-100% for maximal strength (1-3 reps), 75-85% for strength (4-6 reps), 65-75% for hypertrophy (8-12 reps), 50-65% for endurance (15+ reps).