RIR vs RPE: Which Should You Use to Autoregulate Your Training?

Short answer: it doesn't matter much, because RIR and RPE are the same thing wearing 2 different jerseys. On the modern resistance-training scale, RPE 8 means 2 reps in reserve, RPE 9 means 1, and RPE 10 means you could not have done another rep. Pick whichever notation you find easier to think in. The real RIR vs RPE question, the one almost nobody asks, isn't "which scale" but "can you actually feel where failure is?" Mostly you can't, and that is the part of this post worth your time.

RIR (reps in reserve) is your estimate of how many more reps you could have done in a set before hitting true muscle failure (RIR meaning in 60 seconds; the long version is reps in reserve explained). RPE (rating of perceived exertion) on the lifting-specific scale is the same estimate flipped into a 1-10 effort number. Same idea, 2 notations: autoregulation, adjusting today's load to today's body instead of obeying a rigid percentage.

Below: the conversion chart, a goal-by-goal pick, what each notation looks like written into a program, and then the uncomfortable part both scales share, plus how to fix it in practice.

What's the difference between RIR and RPE?

Functionally, almost nothing. On the RIR-based RPE scale that the strength world adopted after Zourdos et al. (2016), RPE is just RIR inverted into a 1-10 score. RPE 10 = 0 RIR. RPE 7 = 3 RIR. The only genuine difference: RPE adds half-point increments. RPE 9.5 means "I couldn't add another rep, but I could have added load", a near-maximal single state that whole-number RIR literally cannot express. That's it. That's the whole difference.

So when someone online frames this as RIR vs RPE like they're rival systems, they've misunderstood the scale. They aren't competing. RPE is RIR with an extra decimal place for heavy singles.

One source of confusion: there is an older RPE, the Borg scale from cardio, which rates whole-body exertion (breathing, how hard it feels overall). That is not the lifting scale. When a strength program says RPE 8, it means the reps-in-reserve scale below, anchored to reps left in the set, not to how out of breath you were.

RIR vs RPE conversion chart

Here's the conversion, straight from the Zourdos scale (Table 2 of the original validation study, popularized in the Ripped Body RPE guide):

To convert in your head: RIR = 10 minus RPE for whole numbers (RPE 8 is 2 RIR, RPE 7 is 3 RIR), and RPE = 10 minus RIR the other way. Half-points only exist on the RPE side.

Save the chart to your phone. Notice how the bottom of it gets vague fast: "4 to 6 reps left" is a wide range, and that vagueness isn't laziness in the table. It's honest. Your perception genuinely gets worse the farther you are from failure, which brings us to the part that matters.

Which is better for hypertrophy vs strength?

If forced to split them by goal: RPE wins for strength and powerlifting, RIR wins for high-rep hypertrophy work. RPE's half-points (9.5) exist precisely to encode load-limited singles near your 1RM, exactly the territory powerlifters live in. For a 5x5 bench at RPE 8, that half-point resolution earns its keep. For bodybuilding, where you're chasing a pump in the 10-15 rep range, "leave 2 RIR" is more intuitive than translating to an RPE number, and the half-points are useless anyway. The target ranges by goal are in how close to failure you should train, and whether you need to go all the way is in is training to failure necessary for hypertrophy.

Does autoregulation itself beat fixed percentages? Yes, and that's settled. A 2025 network meta-analysis of 19 RCTs (438 participants) found every autoregulated method, RPE, velocity-based and APRE, outperformed percentage-based training for 1RM gains. RPE/RIR ranked second for squat. Why? A fixed 80% 1RM is a brutal grind on a bad-sleep day and a warm-up on a great one. RPE/RIR adjusts to your daily readiness. Percentages can't. So whichever notation you choose, you're already ahead of anyone chained to a spreadsheet of percentages.

A quick decision table

How each one looks written into a program

The notation changes the sentence, not the instruction.

• RPE style: "Squat 3x5 @ RPE 8." Work up to the heaviest load that leaves about 2 reps in the tank on the first set, then hold it. If set 1 comes in at RPE 9, take a little weight off for the rest.
• RIR style: "Leg press 3x12 @ 2 RIR." The same instruction as RPE 8, written as reps instead of a score. On machines you'll usually add a rep or 2 to later sets rather than changing the plates.
• Either way, rate the set the moment you rack it, while the last rep is still fresh, not after a 2-minute rest.
• Either way, write the rating next to the weight and reps. A log line that says "100 kg x 8 @ RPE 8" tells you far more next week than "100 kg x 8" (how to track gym progress covers what else is worth writing down).

The weakness both share, and how to fix it

Here's the catch nobody markets: both scales depend entirely on your self-perception, and your self-perception is bad. Not "could be better" bad. Genuinely unreliable bad, especially where you use it most (why your reps-in-reserve estimate is wrong is the long version).

The research is blunt and consistent. Across common exercises, the standard error of predicting reps to failure runs 2.64 to 3.38 reps: leg press 3.38, chest press 2.91, pulldown 2.95 (study here). Translation: when you call a set "2 RIR," true failure was routinely 4-5 reps away. And the error isn't random. Trained lifters systematically underpredict: they stop with gas in the tank. In a Frontiers in Psychology study, people who thought they hit their rep max actually had about 2 more reps in them; their "failure" averaged 11.6-13.3 reps when true failure was 14.1-14.3.

It gets worse the farther from failure you go. In a 70% 1RM squat set averaging about 16 reps, experienced lifters were off by 5.15 ± 2.92 reps when rating their position relative to failure (MASS Research Review). 5 reps. That's not a rounding error; that's a different training stimulus entirely.

The cruel irony: accuracy is good only at 0-2 RIR on heavy, low-rep sets. It falls apart at 3+ RIR and 12+ reps, which is exactly the high-rep hypertrophy zone where lifters lean on autoregulation hardest. Experience helps (experts land within about 1-2 reps, beginners are off by 4-5; see how to calibrate your reps in reserve), but Zourdos's 2019 follow-up showed even at 1 RIR, trained lifters stay imperfect. Proximity helps. It doesn't cure the problem.

So how do you fix a guess? You anchor it to something objective (how to measure reps in reserve walks through the 3 options).

The original Zourdos validation wasn't just a feelings survey: it correlated RPE against average concentric bar velocity at r = -0.88 in experienced squatters. As you fatigue, reps physically slow down. That velocity decay is the external, measurable truth that the subjective scale was trying to approximate all along. It's the basis for velocity-based training, and it's why a barbell encoder beats a guess. An objective anchor matters most exactly where perception is worst: the high-rep, far-from-failure sets where you'd otherwise be 4-5 reps off.

You don't need a barbell sensor to read it. Rep slowdown shows up at the wrist too (how an Apple Watch detects muscle failure covers what a wrist can and can't see).

Riven is the Apple Watch app that scores muscle failure. It reads your wrist motion and stays quiet during the set; about three seconds after you rack the weight you get the exercise, the rep count and a 0-100 score. Reps slow down as a muscle nears failure, and that is what the score is built on. No barbell clip, no camera, no extra hardware. It shows you which set was the real one.

Use an objective readout the way a good coach uses a bar-speed number: not to replace your RPE or RIR call, but to check it. Call the set as you rack it, then compare. Over time you learn which way your calls drift, and on which exercises, and that is what calibrating your RIR actually means.

That's the honest pitch. RIR and RPE both work, autoregulation beats fixed percentages, and the bottleneck isn't your scale, it's your self-perception. Sharpen that with an objective signal and either notation gets a lot more trustworthy.

FAQ

What's the difference between RIR and RPE?

On the modern lifting scale, almost none: they're the same construct. RPE is RIR inverted into a 1-10 number (RPE 8 = 2 RIR). The only real difference is RPE's half-points (e.g. 9.5) for load-limited near-maximal singles, which whole-rep RIR can't express.

How do I convert RPE to RIR?

Subtract from 10. RPE 9 = 1 RIR, RPE 8 = 2 RIR, RPE 7 = 3 RIR, and RPE 10 = 0 RIR, which is failure. RPE 9.5 has no whole-rep RIR equivalent: it means no more reps were possible, but a little more load was.

Is RIR more objective than RPE because it counts reps?

No. Both rely on the identical internal perception of effort. "Reps left" is itself an estimate, not a measurement, and counting it doesn't make it objective. Neither scale is objective; both are subjective.

If I leave 2 RIR, am I really 2 reps from failure?

Usually not. Self-perception error averages 2.6-3.4 reps, and trained lifters tend to undershoot, so "2 RIR" often means true failure was 4-5 reps away. That undershoot silently reduces hypertrophy stimulus on high-RIR sets.

Is percentage-based loading more precise than RPE/RIR?

No. A fixed %1RM ignores daily readiness: it's a different effort on a tired day than a fresh one. In meta-analytic evidence, autoregulated RPE/RIR matched or beat percentage-based training for both strength and hypertrophy.

Can I get more accurate at RIR/RPE?

Yes, it's a trainable skill, not innate. Experts (over 3 years of training) land within about 1-2 reps; beginners are off by 4-5. Practicing near failure helps, and checking each call against an objective anchor like measured rep slowdown gives you feedback to calibrate on.

Is there an objective way to check my RIR or RPE?

Yes. Reps slow down as a muscle approaches failure, and the original RPE scale was validated against exactly that bar-velocity slowdown. A barbell velocity sensor reads it, and so can a device on your wrist. Riven is the Apple Watch app that scores muscle failure; it scores each set the moment you rack it.

Sources

• Zourdos et al. (2016) — Novel Resistance Training-Specific RPE Scale Measuring Repetitions in Reserve, J Strength Cond Res
• "Just One More Rep" — Ability to Predict Proximity to Task Failure in Resistance Trained Persons (Frontiers in Psychology, 2020)
• Ability to Predict Repetitions to Momentary Failure Is Not Perfectly Accurate (PMC5712461)
• Zourdos (2019) — Proximity to Failure and Total Repetitions Influence Accuracy of Intraset RIR-Based RPE (PubMed)
• Autoregulated Resistance Training for Maximal Strength: Network Meta-Analysis (PMC12336695)
• RPE and RIR: The Complete Guide — MASS Research Review
• A Guide To Using RPE and RIR In Your Training — Ripped Body