One Rep Max (1RM) Calculator
Your one rep max (1RM) is the most weight you can lift for a single repetition. This calculator estimates it from a set you've already completed and shows useful training percentages.
How it works
This tool estimates your one rep max from a submaximal set — a weight you lifted for multiple reps. It averages two well-known formulas. The Epley formula is 1RM = weight × (1 + reps / 30). The Brzycki formula is 1RM = weight × 36 / (37 − reps).
Both formulas are most accurate at lower rep counts (about 1 to 10 reps). As reps climb past 10-12, fatigue and technique introduce error, so treat higher-rep estimates as rough guides only.
The percentage table converts your estimated 1RM into common training loads. For example, lifting at 85% of 1RM typically allows about 5-6 reps, useful for building strength.
Tips
Test with a weight you can lift for 3-6 reps for the most reliable estimate.
Always warm up thoroughly and use a spotter or safety equipment before attempting heavy lifts.
Recalculate as you progress — your 1RM changes with training, so update your percentages every few weeks.
FAQ
How accurate is a calculated 1RM?
Estimates are usually within a few percent of a true max when based on sets of 1-6 reps performed with good form. Accuracy drops as reps increase.
Which is better, Epley or Brzycki?
They give similar results at low reps. Epley tends to estimate slightly higher at high reps, Brzycki slightly lower. Averaging them balances the difference.
Should I actually attempt my 1RM?
Not necessarily. Estimating from submaximal sets is safer and avoids the high injury risk of true max attempts, especially without a spotter.