One Rep Max Calculator

You hit five clean reps at 225 on the bench last Saturday and you want to know what that translates to as a one-rep max so you can program percentages for next month's cycle. Actually testing a 1RM is hard on the joints, requires a spotter, and isn't something to attempt every time you want to update your training math.

The Epley, Brzycki, and Lombardi formulas all estimate 1RM from a set taken to or near failure with a known weight and rep count. They diverge a bit at higher rep ranges — Epley is slightly more aggressive, Brzycki conservative, Lombardi handles low reps best. A reasonable approach is to look at all three and use the average, especially if you're using the result to set training percentages where being 5% off doesn't ruin a workout.

The formulas: Epley is weight × (1 + reps/30). Brzycki is weight × (36/(37 - reps)). Lombardi is weight × reps^0.10. Each was derived empirically from observation of trained lifters, and each makes slightly different assumptions about the strength-endurance relationship at moderate rep ranges. For 5 reps, the three formulas typically agree within 3%. At 10 reps, they spread to about 5-7%. Above 12 reps, all three start to overestimate because endurance becomes the limiter rather than maximal strength — so the formulas were never calibrated reliably in that range.

A worked example: you benched 225 lbs for 5 reps. Epley: 225 × (1 + 5/30) = 225 × 1.167 = 262.5 lbs. Brzycki: 225 × (36/(37-5)) = 225 × 1.125 = 253 lbs. Lombardi: 225 × 5^0.10 = 225 × 1.175 = 264 lbs. Average: about 260 lbs. So your estimated 1RM is around 260 — meaning your training percentages would be: 70% = 182, 80% = 208, 90% = 234. For a 5x5 program at 70-80%, those numbers feel right and let you stop second-guessing the working weight.

The limitations are honest: these are estimates, not measurements. Your true 1RM depends on technique, leverages, fatigue, sleep, nutrition, and a dozen other variables on the test day. A formula extrapolating from a 5-rep set can't account for whether the lifter is grinding rep five with bad form or could've done seven with good form. If you actually want to know your 1RM, test it on a fresh day with a competent spotter and proper warm-ups — the formulas are for programming math, not for chasing a real number. Strength programs that use percentage-based loading (5/3/1, Westside, conjugate methods) all build in some forgiveness for the estimate being slightly off because the system self-corrects through autoregulation or AMRAP sets.