How hard was that set? Two scales answer the same question from different angles. Both come from the powerlifting world, both are now standard in hypertrophy and strength programming, and both get used wrong about half the time.
RPE: Rate of Perceived Exertion
RPE is a 1–10 scale. You rate how hard the set felt. RPE 10 = absolute maximum, you couldn’t have done another rep no matter what. RPE 6 = casual, lots in the tank. The scale was originally 6–20 (Borg), but lifting culture stuck with the simpler 1–10 version.
RIR: Reps in Reserve
RIR is more concrete. You estimate how many more reps you could have done with good form before failure. RIR 0 = none, you went to failure. RIR 3 = three more reps were available. RIR is essentially RPE flipped: RPE 10 = RIR 0, RPE 9 = RIR 1, RPE 8 = RIR 2, and so on.
Side-by-side comparison
If you’re thinking “these are basically the same thing,” you’re right.
- RPE 10 / RIR 0: True failure. Could not do another rep with good form.
- RPE 9.5 / RIR 0–1: Maybe one more rep, but it would be ugly.
- RPE 9 / RIR 1: One clean rep left in the tank.
- RPE 8 / RIR 2: Two more clean reps available. The standard prescription for most hypertrophy work.
- RPE 7 / RIR 3: Three more reps. Speed/technique work.
- RPE 6 / RIR 4+: Easy. Warm-up territory.
When to use each
RIR is better when: you’re newer to autoregulation. Counting reps in reserve is concrete and harder to fudge. “Could I have done two more reps of squats at this weight?” is an honest question.
RPE is better when: you’re training higher reps (12+) or doing exercises where rep counting at the limit gets fuzzy. After 15 reps of leg press, asking “how much more was in me” produces noisy answers.
Common mistakes
- Calling everything RPE 10. Most lifters who think they’re going to failure are stopping at RPE 8.5 with bad form. Real RPE 10 happens about once a month, in a pre-programmed test.
- Calling everything RPE 8. The opposite problem. If your “RPE 8” bench takes 20 minutes between sets and your form breaks, that was RPE 9.5+.
- Using RPE without progress tracking. The point of RPE/RIR is to compare. Same weight, fewer reps with same RPE next session = you’re fresher than usual. Same weight, more reps at same RPE = you’re getting stronger. Without recording it, the data is noise.
- Hitting RPE 9–10 every set. Hammers your CNS, drives down volume tolerance, accelerates burnout. Most working sets should be RPE 7–8 with the last set or two at 8–9.
How GymTrainr uses both
The app asks for RPE on every set you log. Over time it builds an accurate picture of your true effort capacity, which feeds the AI’s next-session recommendations: lighter loads when you’ve been hovering at RPE 9+, more weight when you’re cruising at RPE 6–7. That’s how progressive overload should actually work.