What Is a One-Rep Max?
Your one-rep max (1RM) is the heaviest weight you can lift for a single clean repetition — the anchor number for every percentage-based strength programme. Testing it directly is taxing and risky, so lifters estimate it from a hard sub-maximal set instead. This calculator converts one all-out set into a 1RM estimate using the three most validated formulas, then builds the percentage table your programme runs on.
How the calculator works
You enter the heaviest weight you can lift for a clean set of 1–20 reps. The calculator runs three published formulas — Epley (weight × (1 + reps/30)), Brzycki (weight × 36/(37 − reps)) and Lombardi (weight × reps^0.10) — and averages them. Below the estimate you get a full training-percentage table from 50% to 95% with the typical rep target at each load.
Common use cases
- Setting training loads for 5/3/1, Texas Method or any percentage-based programme
- Testing progress without grinding out a true single
- Comparing strength across bodyweights with a training partner
- Planning peaking blocks around 90–95% loads
Formula & accuracy
All three formulas agree within a few percent below about 10 reps; above 10 reps estimates drift high because fatigue, not strength, starts limiting the set. For best results use a set of 3–6 reps at a weight you could not lift more than once more.
Enter weight in pounds; for kilograms multiply the result by 0.4536.
Safety notes
Estimated maxes are not invitations to test a true single. Keep a spotter, warm up progressively, and leave one rep in reserve on heavy working sets.
Frequently Asked Questions
How accurate is a calculated one-rep max?
Within 2–5% of a tested 1RM when you use a hard set of 3–6 reps. Sets above 10 reps overestimate because muscular endurance becomes the limiter.
Which formula should I trust?
The calculator averages Epley, Brzycki and Lombardi. Epley is the most widely used; Brzycki tends to read slightly lower at higher rep counts.
How often should I retest?
Every 4–8 weeks is plenty for a working estimate — retesting too often adds fatigue without information.
Does it work for bench press, squat and deadlift?
Yes — the formula is lift-agnostic. We also offer dedicated bench press, squat and deadlift max calculators with lift-specific guidance.
Privacy & Your Data
StatPlay runs entirely in your browser. The numbers you enter never leave your device — there is no server, no account and no upload. We store only a single local preference flag when you dismiss the cookie notice.