1RM stands for one repetition maximum. It is the amount of weight that you can lift only once with perfect form. Typically your one rep max is measured by a few basic exercises such as the squat or bench press, but it can be tested using any exercise.
You want to measure it so you know what weight to lift when you first start your program. Read on to find out more.
More often than not, your 1 rep max is the standard tool professional trainers use for measuring results and gains in strength. 1RM needs to be determined before you start an exercise program, when switching an exercise program, and/or when testing for results.