1RM Calculator
Estimate your one-rep max from any working set. Epley, Brzycki, Lombardi, O’Conner formulas — free, no signup.
Training percentages
About this calculator
A one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. Testing a true 1RM is fatiguing and risky, so most athletes estimate it from a heavier set instead. Plug in any set of 1–10 reps and this calculator returns an estimate using four standard formulas. Epley is the most common, Brzycki tends to be slightly more conservative at higher rep counts, Lombardi and O’Conner give you a range to sanity-check against. Estimates get less reliable past 10 reps — if your best set was 15–20 reps, treat the number as a rough ceiling, not a target.
Sources
Epley (1985), Brzycki (1993), Lombardi (1989), O’Conner et al. (1989).
FAQs
How accurate is a 1RM estimator?
Within roughly 5% for sets of 1–5 reps for trained lifters. Accuracy drops as rep count rises — sets above 10 reps are educated guesses, not predictions.
Which formula should I use?
Epley is the default and matches most programming spreadsheets. Use Brzycki if you find Epley overestimates at higher reps. Compare all four to gauge confidence.
Can I use this for any lift?
Best results for compound barbell lifts (squat, bench, deadlift, overhead press). Isolation exercises behave less predictably because technique fatigue dominates before strength does.
Should I actually test my 1RM?
Rarely. Most athletes use an estimated 1RM (e1RM) to set weekly percentages and never max out. True testing belongs to meet prep or a planned strength block.