How 1RM is estimated
Your one rep max is the heaviest weight you can lift once with good form. Rather than risk a true max attempt, formulas predict it from a heavier set of a few reps:
- Epley: weight × (1 + reps ÷ 30)
- Brzycki: weight × 36 ÷ (37 − reps)
- Lombardi: weight × reps^0.10
We average all three. They agree closely between 2 and 10 reps and drift apart beyond that.
Using the percentage chart
Most strength programs prescribe weights as a percentage of 1RM. Strength work usually sits at 80–90% for 3–6 reps, muscle building at 65–80% for 6–12 reps. Base your numbers on a recent set taken close to failure.
Frequently asked questions
How accurate are 1RM calculators?
Within about 5% for most people using sets of 2–10 reps close to failure. They're less accurate for very high reps or for lifters with unusual strength endurance.
Which formula is best?
None is best for everyone. Brzycki tends to be accurate at low reps and Epley at moderate reps, which is why averaging them is a good default.
Should I test my true one rep max?
Only if you're an experienced lifter with a spotter or safety bars. For most training, an estimated max works just as well and is safer.
These results are estimates for healthy adults and are not medical advice. If you are pregnant, breastfeeding, under 18, or managing a medical condition, talk to your doctor or a registered dietitian.