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One-rep max

Also called 1RM, one rep max, 1 rep max

A one-rep max, or 1RM, is the heaviest weight you can lift for one full rep of an exercise, and no more.

Did not go100 kg
A bar loaded to 100 kg: one rep goes up, a second will not. That is a 100 kg one-rep max; 80% of it is 80 kg.

In plain words

The number belongs to one exercise. Your squat one-rep max and your bench press one-rep max are different numbers. Two kinds go by the name. A tested max is a real lift: you load the bar and take a single. An estimated one is worked out from a lighter set of several reps with a formula. Programs set loads against it: 80% of 1RM means 80 kg for a lifter whose max is 100 kg. A 2020 systematic review of 32 studies and 1,595 people found the test repeats well: a median test-retest correlation of 0.97, and a median variation of 4.2% between tests.

An example

A bar loaded to 100 kg. You press it once and the second rep does not go up. Your bench press one-rep max is 100 kg. The weight either went up or it did not, and that is what makes this a tested max rather than an estimate. A program written in percentages reads off it, so a set at 80% is 80 kg and a set at 60% is 60 kg.

Often confused with

Estimated 1RM A one-rep max is lifted; an estimated one is calculated from a set of several reps. PR A personal record is your best so far at anything; a one-rep max is only the heaviest single.
Estimated 1RM An estimated 1RM, or e1RM, is a calculated guess at your one-rep max, worked out from a set of several reps with a formula instead of a heavy single.
Rep max A rep max is the heaviest weight you can lift for a given number of reps and no more: a 5RM is the most you can lift five times.
Epley formula The Epley formula estimates a one-rep max from a set of several reps: one-rep max = weight × (1 + reps ÷ 30).
Percentage of 1RM A percentage of 1RM is a way to set a weight as a share of your one-rep max.
PR A personal record, or PR, is the best you have ever done at something in the gym: the heaviest weight, the most reps at a weight, the highest estimated max.

Go deeper

Are one-rep max calculators accurate? One-rep max calculators are close, not exact. Epley and Brzycki side by side from 2 to 12 reps, what studies found about error, and three rules for the number. Updated

Sources

  1. Grgic et al. 2020. Test-retest reliability of the one-repetition maximum (1RM) strength assessment: a systematic review. Sports Med Open 6(1):31 Read

Updated . How these pages are researched and corrected: editorial policy. Every term in the glossary.