What is a One Rep Max?
Your One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise. It is the gold standard for measuring raw strength in powerlifting, weightlifting, and general strength training.
However, constantly testing your true 1RM is dangerous and heavily taxes your central nervous system. Instead, strength athletes use predictive mathematical formulas to estimate their 1RM based on how many reps they can perform with a sub-maximal weight.
The Epley Formula
There are several formulas used to estimate 1RM (such as Brzycki, Lombardi, and O'Conner), but the Epley formula is widely considered the most accurate for the general lifting population.
The Formula
To find your estimated 1RM, the calculation uses the Weight Lifted () and the Number of Repetitions ():
1RM = w(1 + r/30)
Using Your 1RM for Training
Once you know your 1RM, you can program your training effectively. Most professional strength programs (like 5/3/1 or Smolov) dictate your daily lifting weight as a specific percentage of your 1RM. For example, if your 1RM is 300 lbs, a "hypertrophy" day might call for 5 sets of 10 reps at 65% of your 1RM (195 lbs).