What a one-rep max is
Your one-rep max (1RM) is the most weight you can lift once with good form. Testing it directly is risky, so lifters estimate it from a set of several reps. This tool uses the Epley formula (weight × (1 + reps/30)) and cross-checks with Brzycki.
Why estimate instead of test
A true max attempt is taxing and injury-prone, especially without a spotter. Estimating from a 3–8 rep set is safer and accurate enough to program your training around.
Programming with percentages
Most strength programs prescribe work as a percentage of 1RM — heavy singles near 90%, hypertrophy around 70–80%. The tool shows those percentages so you can pick working weights straight away.
Frequently asked questions
How many reps give the best estimate?
Sets of about 3–8 reps are most accurate. Very high-rep sets drift because endurance, not just strength, starts to matter.
Epley or Brzycki?
They're close for low reps and diverge a little higher up. The tool shows both so you can see the range rather than trust one number.
How do I calculate my one-rep max?
Enter a weight and the reps you did with it; the tool estimates your 1RM with standard formulas like Epley: 1RM = weight × (1 + reps/30).
How accurate is an estimated 1RM?
It is a good estimate for sets under about 10 reps; accuracy drops as reps climb, since endurance starts to matter more than strength.
Why estimate 1RM instead of testing it?
Estimating from a lighter set is safer — a true max attempt carries more injury risk, especially without a spotter.