By Coach Jeff Alagar, NASM Physique and Bodybuilding Coach and ISSA Certified Nutritionist. Updated November 2026.
Your one-rep max (1RM) is the heaviest weight you can lift once with good form. You can estimate it safely from a set of 3 to 8 reps instead of testing a true max.
How this one-rep max calculator works
The result averages the Epley (weight x (1 + reps/30)) and Brzycki (weight x 36 / (37 minus reps)) formulas. The chart converts your 1RM into training loads at common percentages, rounded to the nearest 1.25 kg so you can load the bar.
Frequently asked questions
How often should I test my 1RM?
Most lifters do not need to. Re-estimate from your working sets every 4 to 8 weeks.
What percentage of 1RM builds muscle?
Anything from about 30 to 85% builds muscle when sets are taken close to failure. 65 to 80% (6 to 12 reps) is the most time-efficient for most people.
Related calculators
These calculators give general estimates for healthy adults and are not medical advice. If you are pregnant, under 18, or have a medical condition, ask your doctor before changing your diet or training.
