The RPE-Based 1RM Calculator is a modern tool for lifters who use Rate of Perceived Exertion to guide their training. Instead of training to failure, RPE allows you to rate the difficulty of a set on a scale of 1 to 10. By telling the calculator how many reps you had 'in the tank' (e.g., an RPE of 8 means you had 2 reps left), it can provide a much more accurate estimated 1RM (e1RM) than formulas that assume you went to failure. This is perfect for modern, sub-maximal training approaches.