One-Rep Max Calculator
Calculate an estimated one-rep max (1RM) from the weight you lifted and how many reps you did.
How to use the one-rep max calculator
- Enter the weight you lifted.
- Enter how many reps you managed with that weight.
- Your estimated one-rep max (1RM) updates automatically, using two different formulas.
What is one-rep max (1RM)?
One-rep max (1RM) is the heaviest weight you could theoretically lift a single time with correct form. Instead of actually testing this (which is demanding and carries injury risk), 1RM can be estimated from a lighter weight you can lift for several reps. This calculator shows two widely used formulas: Epley (1RM = weight × (1 + reps/30)) and Brzycki (1RM = weight × 36 / (37 − reps)).
Frequently asked questions
Why do Epley and Brzycki give slightly different results?
Because they're derived from slightly different datasets and mathematical approaches to the relationship between weight and reps. The difference is usually small at low rep counts, but increases somewhat at higher reps.
Why shouldn't I just test my 1RM directly?
Lifting a maximal weight once requires proper warm-up and correct technique under heavy load, and carries a higher injury risk than submaximal lifts. An estimate from 3-8 reps is safer and usually precise enough for training planning.
What is 1RM used for in practice?
1RM is often used as the basis for planning training weights as a percentage of max (e.g. "80% of 1RM" for strength sessions), and as a comparison metric for progress over time.