RIR vs RPE in Strength Training

RIR and RPE describe one thing — how close the set was to failure — from opposite directions. RIR counts what you left behind. RPE grades what it cost. Enter a set below and the calculator prints both, along with what the set was worth as a share of your max.

The conversion, and its limits

RIR	RPE
0 (failure)	10
1	9
2	8
3	7

Inside that block the arithmetic is simply RPE = 10 − RIR. Below RPE 7 it stops being exact: the published lifting scale bundles four, five and six reps in reserve into a single 5-to-6 band, and uses plain effort descriptions under that. So “RIR 5 equals RPE 5” is a convenient shortcut, not what the source table says.

Two different family trees

The original RPE scale is Gunnar Borg’s, developed more than four decades ago and running from 6 to 20 — the odd range exists because the numbers were meant to roughly track heart rate in beats per minute, which is a sensible idea for aerobic work and a useless one for a set of squats. Borg later produced a category-ratio scale from 1 to 10, and the OMNI scale followed. Those 1-to-10 scales are the ancestors of the lifting RPE you see in programs today.

The repetition-anchored version is younger and was built for a different problem. Grading a set of five heavy squats on a general effort scale asks for a judgment; asking how many reps were left asks for a count.

The failure the count catches

There is a documented flaw in traditional effort ratings applied to lifting: lifters frequently report a less-than-maximal score even when they performed the maximum possible number of repetitions at that load. The set was maximal; the rating was not. Anchoring the scale to reps in reserve makes that mismatch checkable — a lifter who says “two left” can be asked to prove it, and often cannot.

That advantage is largest exactly where it matters, at near-limit loads, which is why programs that prescribe heavy work by feel tend to use the repetition-based version.

Pick one and stay with it

Both scales work; switching between them mid-program does not, because your personal calibration is what makes either of them useful. If you already think in effort scores, keep them. If you already count reps, count reps.

Read what each number stands for on the reps in reserve scale, turn a rating into a load on how to use reps in reserve, or convert effort into a share of your max with the RPE to percentage chart.

This content is informational and does not replace coaching.