1RM Calculator

1RM: estimating your maximum strength

Your 1RM (One Rep Max) is the heaviest load you can move for a single rep, and it's the number most strength programs are built around. A few formulas get used over and over. Epley 1RM = weight · (1 + reps/30); Brzycki 1RM = weight · 36/(37 − reps); Lombardi 1RM = weight · reps^0.10; and Lander 1RM = (100·weight)/(101.3 − 2.67123·reps). They hold up well in the 1-10 rep range and start to wobble past 12. Example: 80 kg × 5 reps through Epley gives 80 · (1 + 5/30) = 80 · 1.167 ≈ 93.3 kg. Going for a true 1RM is draining and risky if you're new to lifting, which is why estimating from a submaximal set tends to win out.

Applications: percentage-based training and bodybuilding

Percentage-based programs lean on it heavily, whether that's Jim Wendler 5/3/1, Westside Conjugate or Sheiko, all of which prescribe loads as a slice of your 1RM. So do bodybuilding plans organized around %1RM bands (hypertrophy in the 65-85% area, strength 85-95%) and RPE-based powerlifting meets, where it helps call openers and attempts. Coaches like it for tracking progress across mesocycles too, since it spares the lifter from risky max-out days.

FAQ

Which formula is most accurate? Up to 10 reps, Epley and Brzycki land in roughly the same place. Beyond that they all run high, and Lombardi usually comes out the most conservative on longer sets.

Should I test my 1RM directly? Only if you've got some experience, a spotter and a solid warm-up behind you. For most people, estimating from 3-5 reps is the safer call and close enough.

Does the estimate work for any exercise? It shines on the big compounds (squat, bench, deadlift, overhead press). On isolation work it gets shaky, because technique and fatigue start calling the shots.

How often should I update my 1RM? Roughly every 4-8 weeks, or sooner if the prescribed percentages start feeling too light or too heavy.