Calculator Strength
One-rep max calculator
Your one-rep max (1RM) is the most weight you could lift for a single rep. You don’t have to actually test it — enter a set you’ve done and this estimates your 1RM with the Epley formula, then gives you the training percentages to program from.
Estimated one-rep max
0lb
Training percentages
| % of 1RM | Weight | Typical reps |
|---|
By the numbers Context
How a one-rep max is estimated
The one-rep max is the standard yardstick for strength: the most weight you can move for a single clean repetition. Testing it directly is taxing and, for many lifters, risky, so it is usually estimated instead — from a set taken close to failure at a lighter weight. This calculator applies the Epley formula, one of the most widely used estimation equations.
The maths works because reps and weight trade off predictably: the more reps you can do with a given load, the higher your true one-rep max. That relationship holds well up to about ten reps and drifts beyond it, so a set of three to eight reps gives the most reliable estimate. Once you have a number, you can program training as percentages of it — for example, sets around 70–80% for building muscle.
Epley
the common 1RM formula: weight × (1 + reps ÷ 30)
1985
≤10 reps
where the estimate stays most accurate
Research
Sources: Epley and Brzycki one-rep-max estimation formulas; strength-training research.
Frequently asked questions
What is the formula for one-rep max?
A common one is the Epley formula: 1RM = weight × (1 + reps ÷ 30). Several similar formulas (like Brzycki) exist and give close results. This calculator applies one for you.
How do I calculate my 1RM?
Take a weight you can lift for a few clean reps to near failure, then enter the weight and the number of reps. The calculator estimates the single-rep max from that submaximal set — no all-out attempt needed.
What is my max if I bench 225 for 5 reps?
Using the Epley formula, 225 for 5 reps estimates a one-rep max of about 262 lb (225 × [1 + 5 ÷ 30]). Enter your own numbers for a personalised estimate.
How accurate is a 1RM calculator?
Quite accurate for sets of about ten reps or fewer. Above that, small errors grow, so a set of three to eight reps gives the most reliable estimate.
Why train with percentages of 1RM?
Because different goals map to different intensities — roughly 70–80% of 1RM for building muscle, higher for pure strength. Knowing your 1RM lets you pick weights that match the goal.