What does 1RM mean?
One rep maximum (or 1RM) is an estimate of your best possible single rep lift for an exercise. We use it because it is helpful as a single number to use when comparing different sets from a workout. Many popular workout programs are based on a percentage of your 1RM as you progress, rather than giving specific weights to use.
We use the Brzycki formula to estimate your 1RM. We have found it to be the best way to calculate your 1RM.