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One-rep max (1RM) calculator
Enter a weight and the reps you did with it — get an estimated 1RM, a full percentage table, and exactly which plates to load per side. Runs entirely in your browser.
Training percentages, explained
| % of 1RM | Typical use | Usual rep range |
|---|---|---|
| 90–100% | Max-strength / peaking work | 1–3 reps |
| 75–89% | Strength building | 3–6 reps |
| 60–74% | Hypertrophy (muscle growth) | 6–12 reps |
| Below 60% | Technique, warm-up sets, deload weeks | 12+ reps |
Frequently asked questions
How is estimated one-rep max (1RM) calculated here?
This calculator averages three widely-used formulas — Epley (weight × (1 + reps / 30)), Brzycki (weight × 36 / (37 − reps)), and Lombardi (weight × reps^0.10) — because any single formula drifts more as reps climb. The average tracks closer to a real tested max across the 1–12 rep range these formulas are built for.
Why do the three formulas disagree?
Epley assumes a roughly linear drop-off in strength per rep, Brzycki assumes it curves, and Lombardi is a pure power-law fit to older barbell-lift data. They agree closely at 1–5 reps and spread apart above 8–10 reps, which is also where any estimate gets less reliable — treat a 1RM estimated from a 10+ rep set as a rough ceiling, not a number to load up and attempt cold.
What do the plate numbers mean?
Each row shows the plates to load on one side of a standard barbell (the other side is loaded identically) to hit that percentage of your estimated 1RM, assuming a 20 kg / 45 lb Olympic bar and a standard plate set. Weights are rounded down to the nearest loadable increment, so the actual bar weight may be a touch below the displayed target.
Is this a substitute for a real 1RM test?
No. A true 1-rep max is only measured by actually lifting it, ideally with a spotter and good form. This calculator gives a safe, no-attempt estimate for programming percentage-based training (5/3/1, linear periodization, etc.) between real max-testing sessions.