RIR vs RPE in strength training

Search for an RPE scale and you will often find the Borg scale, created by the Swedish psychologist Gunnar Borg. Its best-known version runs from 6 to 20 and rates how hard your whole body is working, which is why it is used in endurance training, exercise testing and healthcare. The lifting scale is a different and much newer scale that counts reps left in one set.

A number above 10 is Borg. If a program writes RPE 8 next to sets and reps, it means two reps left.

On the lifting scale they are one measurement written two ways: RPE 8 and RIR 2 describe the same set. The difference is in how the question feels when you ask it.

RIR asks you to count: how many more reps could I have done with the same technique? Counting is concrete, which makes RIR the easier one to start with, and it is how most research on muscle growth describes how close to failure a set went.

RPE asks you to rate: how hard was that set, out of ten? It came to lifting through powerlifting coaching, and in 2016 Zourdos and colleagues published and tested a version tied to reps in reserve. Lifters who prefer it point to two things: half points near the top, which suit heavy singles at RPE 8 or 9, and charts that pair each RPE and rep count with a percentage of the 1RM, so a heavy set gives an estimated max. Helms and colleagues print such a chart and warn that it is a guide, not an exact conversion.

Use whichever your program is written in. If you write your own, RIR is simpler to read in the gym. Nothing is lost either way, because the conversion is exact.

1. Rate right after the last rep, before you rest. A minute later the set already feels easier than it was.
2. Rate working sets, not warm-ups. The scale is most useful from RPE 7 upwards, three reps left or fewer.
3. Count only reps you could have done with the same technique and range of motion. A grinding rep that would break your form is not in reserve.
4. Use whole numbers until you can tell two reps left from three. Then add half points if your program uses them.
5. Write the number next to the weight and reps, so you can compare it the next time you do the exercise.

Close, but not exact. A 2022 meta-analysis of 12 studies with 414 participants found that people underestimated how many reps they had left by about one rep on average (0.95). Estimates were better in sets of 12 reps or fewer, in later sets of an exercise, and slightly better the closer the set came to failure.

Experience helps less than you might think. In the squat study that introduced the scale, experienced lifters rated a true 1RM 9.8 on average against 9.0 for novices. Yet the meta-analysis found no effect of training status, and in a six-week bench press study, trained men did not get significantly more accurate.

So check yourself now and then. Call your RIR at the rep where you would normally stop, then keep going in the same set until you cannot do another clean rep: if you called RIR 2 after 8 reps, you should reach about 10. Do it only where failing is safe: machines, dumbbells, or a barbell with safety arms set. Helms and colleagues suggest that newer lifters record their RIR without basing weights on it until their estimates hold.

The number becomes useful when it decides the weight. Say your program asks for 3 × 8–12 at RIR 2 in the goblet squat and you start at 20 kg:

Next time, start at 24 kg. When every set reaches 12 reps with about two still in reserve, add the smallest step you can and work back up through the range.

If a set lands two or more reps away from the target, change the weight for the next set rather than waiting for the next workout. If you cannot reach the bottom of the range at the target, the weight is too heavy for today.

For muscle growth, a 2023 meta-analysis of 15 studies found at most a trivial advantage for sets taken to failure, and no clear advantage when failure meant the point where another rep could not be completed. A 2024 series of meta-regressions found growth rising as sets ended closer to failure, while strength gains were similar across a wide range of reps in reserve.

That leaves room. Helms and colleagues suggest two to four reps in reserve on the main lifts, zero to two on other exercises for muscle growth, and sets to failure only on low-risk isolation exercises. Strengthara's ready-made programs sit in the same range: RIR 3 on the heavy 5 × 5 lifts, 2 on most exercises and 1 on small isolation exercises.