THE NUMORIX GUIDE
How to use the One Rep Max Calculator
Last reviewed September 14, 2026
What this calculator does
The engine estimates one-repetition maximum independently with three equations: Epley = weight x (1 + reps / 30), Brzycki = weight x 36 / (37 - reps), and Lombardi = weight x reps^0.
Formula and method
The engine estimates one-repetition maximum independently with three equations: Epley = weight x (1 + reps / 30), Brzycki = weight x 36 / (37 - reps), and Lombardi = weight x reps^0.1. Each estimate is rounded to one decimal place, and the UI uses Epley as the headline result.
Variables and inputs
Weight Lifted is a numeric load in whatever unit you choose; the form has no unit selector and performs no lb-to-kg conversion. Reps is a positive repetition count. The UI accepts values below 37, although these equations are intended for genuine, controlled repetitions rather than arbitrary fractional inputs.
Worked example
For 185 lb lifted for 5 reps, Epley = 185 x (1 + 5 / 30) = 215.8 lb, Brzycki = 185 x 36 / (37 - 5) = 208.1 lb, and Lombardi = 185 x 5^0.1 = 217.3 lb. The page therefore leads with 215.8 and shows the other two estimates for comparison.
How to interpret the result
The result is a training estimate of the load you might lift once under similar conditions, not a tested maximum. The spread between the three values shows formula uncertainty; it is more useful for choosing a conservative training percentage than for declaring an exact strength limit.
Common mistakes to avoid
Keep the load unit consistent when comparing sessions, and do not enter the total weight of several exercises as one lift. Do not use 37 or more reps because the Brzycki denominator reaches zero or becomes negative. A set taken far from failure will usually understate the strength estimate.
Assumptions and limitations
These equations assume a strength-oriented set and do not account for technique, range of motion, equipment, fatigue, body position, or whether the lift is safe to test. They are not a substitute for a qualified coach or a spotter, and a predicted maximum should not be used as permission to attempt a risky load.