One Rep Max (1RM) Calculator
Your one-rep max is the heaviest weight you could lift for a single rep with good form. Estimating it from a lighter set lets you program percentages, track strength, and compare lifts without the injury risk of an actual max attempt. It works for squat, bench, deadlift, and any other barbell lift.
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How it's calculated
This calculator runs two of the most validated 1RM prediction equations and averages them. The Epley formula estimates your max as weight × (1 + reps ÷ 30): a 100 kg set of 5 predicts a 116.7 kg max. The Brzycki formula estimates it as weight × 36 ÷ (37 − reps), which gives the same answer at 10 reps but slightly lower predictions at low rep counts. Because each formula has its own bias, the average of the two is a more stable estimate than either alone.
Both equations were built from observed relationships between rep counts and maximal loads in trained lifters. Their accuracy is best for sets of 10 reps or fewer taken close to failure — beyond 10 reps, the relationship between reps and max load gets noisy because muscular endurance starts to matter more than maximal strength. That is why the calculator caps input at 20 reps and why a set of 3-6 hard reps gives the most reliable prediction.
The result also includes 90% of your estimated max. That is a practical top single for heavy training days: heavy enough to count as near-maximal practice, light enough to leave in the tank. If you train with percentage-based programs, base your working percentages on this estimated 1RM and re-test the estimate every few weeks with a hard set rather than a true max.
Frequently asked questions
How accurate are 1RM calculators?
Within roughly 2-5% for sets of 10 reps or fewer taken near failure. Accuracy improves at lower rep counts — a hard set of 3 predicts better than a set of 10.
Which is better, Epley or Brzycki?
Neither is universally better. Epley tends to predict slightly higher at low reps, Brzycki slightly lower. This calculator shows both and averages them for a more stable estimate.
Should beginners test a true 1RM?
Usually not. An estimated 1RM from a submaximal set gives beginners everything they need for programming without the technique breakdown and injury risk of a maximal attempt.
How often should I re-calculate my 1RM?
Every 4-6 weeks is plenty. Re-run the estimate after a hard top set of 3-5 reps rather than maxing out, and adjust your training percentages from the new number.
Take it with you
Every calculator, plus workout and macro tracking, in the ElevenSix Fitness app for iPhone.