RPE, or rate of perceived exertion, is a 1 to 10 scale for rating how hard a set felt. A 10 means you hit failure and couldn't have done another rep. A 9 means you had one rep left, an 8 means two, and so on. Lifters use it to dose intensity by feel instead of locking every set to a fixed percentage of their max.
Why it matters
Your strength isn't the same every day. Sleep, stress, food, and the last three sessions all move the needle, sometimes by 5 to 10 percent. A fixed percentage program ignores all of that. RPE doesn't. On a rough day, RPE 8 might be 185 pounds instead of 205, and that's the right call. The scale maps directly to reps in reserve, so "RPE 8" and "2 RIR" describe the same set from two directions. Same information, different accent.
How to use it in training
Start by anchoring the top of the scale. Take a safe machine exercise to actual failure once, so you know what a true 10 feels like. Most people who've never done that overestimate their effort by two or three reps.
Then run most working sets at RPE 7 to 9. Rate each set right after you rack the weight, and be honest. If the bar speed on your last rep was still crisp, that wasn't a 9. Expect your ratings to be shaky for the first few weeks. That's normal, and the skill sharpens fast with practice.
Related terms
Go deeper
Want the research on how close to failure you actually need to train? Read our full breakdown: Training to failure vs reps in reserve.