One Rep Max (1RM) Calculator — Epley, Brzycki & Lombardi
Free one-rep max calculator — enter weight and reps to get your estimated 1RM via Epley, Brzycki, and Lombardi formulas. Unit-agnostic (kg or lb). No sign-up.
Type the weight you lifted and how many reps you got. The calculator returns your estimated one-rep max using three standard formulas — Epley, Brzycki, and Lombardi — so you can see how the estimates compare.
What is a 1RM?
Your one-repetition maximum (1RM) is the heaviest weight you can lift once with good form. It’s the gold standard for measuring maximal strength and the number most training loads are based on.
Testing your true 1RM directly is demanding: it requires a warm-up, progressive attempts, a spotter, and carries a non-trivial injury risk even for experienced lifters. That’s why sub-maximal estimation exists: you lift a lighter weight for as many reps as you can, and a formula projects what your 1RM probably is.
The three formulas
Epley (1985)
1RM = weight × (1 + reps / 30)
The oldest and most widely cited 1RM formula. Derived from collegiate football players performing back squats. Works well for moderate rep ranges (3–12).
Brzycki (1993)
1RM = weight × 36 / (37 − reps) (only valid for 1 ≤ reps ≤ 36)
Slightly more conservative than Epley for higher-rep sets. Popular in strength-coaching literature. Undefined at reps ≥37 because the denominator hits zero.
Lombardi (1989)
1RM = weight × reps^0.10
A logarithmic model that tends to sit between Epley and Brzycki for most rep ranges. Used in some strength-training apps.
How the numbers compare
| Weight | Reps | Epley | Brzycki | Lombardi |
|---|---|---|---|---|
| 100 kg | 10 | 133.3 kg | 133.3 kg | 125.9 kg |
| 100 kg | 5 | 116.7 kg | 112.5 kg | 117.5 kg |
| 100 kg | 3 | 110.0 kg | 105.9 kg | 111.6 kg |
| 100 kg | 1 | 103.3 kg | 100.0 kg | 100.0 kg |
| 80 kg | 8 | 101.3 kg | 99.3 kg | 98.5 kg |
At low reps (1–3) the formulas spread wider; above ~8 reps they converge.
Accuracy caveats
- These formulas were regressed on trained athletes doing compound barbell lifts (squat, bench press, deadlift). Accuracy drops for machine exercises, isolation movements, and absolute beginners.
- Reps above 12–15 introduce more error — the relationship between strength and endurance gets noisier.
- Use the estimate as a training reference, not a competition target. If you plan to attempt a true 1RM, work up to it over several sessions.
Unit-agnostic math
This calculator doesn’t convert between kg and lb — it doesn’t need to. If you enter 100 kg and 10 reps, you get ~133 kg back. If you enter 220 lb and 10 reps, you get ~293 lb back. The arithmetic is the same.
Worked examples
-
100 kg for 10 reps — classic training set
Epley: 133.3 kg, Brzycki: 133.3 kg, Lombardi: 125.9 kg.
-
185 lb for 5 reps
Epley: 215.8 lb, Brzycki: 208.1 lb, Lombardi: 217.3 lb.
Frequently asked questions
What is a one-rep max?
Your 1RM is the heaviest weight you can lift for a single repetition with proper form. It's a benchmark most strength programs use to set training loads. A true 1RM test is taxing and carries injury risk, so most lifters estimate it from a sub-maximal set — that's what this calculator does.
Why three formulas instead of one?
No single equation fits everyone. Epley is the oldest and most widely used; Brzycki is slightly more conservative (lower estimates for higher reps); Lombardi uses a logarithmic model that often sits between the two. The differences are small — typically 1–5 kg — but they show the inherent uncertainty in sub-maximal estimation. The point of this page is letting you see all three side by side.
How accurate are these estimates?
±5% for most people, better for reps ≤10. The formulas were derived from athletes doing controlled lifts, so accuracy drops as you get further from that population (very inexperienced lifters, very high reps, machines vs. barbells). Treat the number as a starting point, not a prescription.
Does the formula work the same for kg and lb?
Yes — the math is unit-agnostic. If you enter pounds you get pounds back; if you enter kilograms you get kilograms back. The relationship between reps and max effort doesn't care about the unit system.
What if I can do 37 or more reps?
The Brzycki formula is undefined at reps ≥37 (division by zero). For very high-rep sets, the Epley and Lombardi formulas are still usable, but the relationship between reps and max strength gets weaker above ~20 reps — endurance starts to dominate.
Which formula should I use?
Many coaches default to Epley because it's simple and well-studied. If you're a powerlifter or Olympic lifter (low reps, heavy loads), Brzycki often gives the most realistic numbers for reps ≤6. Lombardi is newer and correlates well for moderate rep ranges. The three usually agree within a few percent — pick one and be consistent.
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