RPE vs RIR: What's the Difference and Which Should You Use?
RPE and RIR are two ways of writing the same thing: RIR is approximately 10 minus RPE. RIR asks you to count reps left, RPE asks you to rate effort — the difference is practical, not physiological, and both carry the same estimation error, which is smallest close to failure.
Key takeaways
- They are the same judgement expressed two ways: RIR ≈ 10 − RPE [1].
- RIR asks you to count ("how many more?"); RPE asks you to rate ("how hard?"). That difference is practical, not physiological.
- Both rest on the same skill, and that skill is most accurate close to failure [3] and improves with practice [7].
- No study compares prescribing by RPE against prescribing by RIR head to head — pick the one you will apply consistently.
- Outcomes are similar across a range of proximities to failure [4][5], so the choice matters less than the consistency.
If you have read that RPE and RIR are different systems, they are not. The RPE scale used in strength training was defined in terms of reps in reserve: RPE 10 is zero reps left, and each point below is roughly one more rep you had in the tank [1]. The two numbers carry the same information.
So the real question is not which is more accurate. It is which question you answer better in the moment, and which one writes a clearer instruction in a program.
The difference in practice
| RIR | RPE | |
|---|---|---|
| The question | How many more reps could I have done? | How hard was that, 1–10? |
| Direction | Counts up from failure | Rates down from a limit |
| Easier when | You can picture the next rep | You are comparing to recent sets |
| Writes well as | “3 × 8, stop at 2 RIR” | “Top set at RPE 8, then back-offs” |
| Awkward when | Far from failure — you are guessing at 6+ | Half points start to feel invented below RPE 7 |
The scale was introduced precisely so that effort ratings could be used to prescribe and autoregulate load, rather than just to describe a session afterwards [2]. Both forms serve that; they differ in ergonomics.
Which should you use?
RIR 1–2 on most working sets
For hypertrophy the evidence supports training reasonably close to failure, with diminishing returns and rising fatigue cost from actually reaching it on every set.
Caveat: Closer to failure is more fatiguing per set — if total weekly volume suffers, you have gone too close.
Deterministic — the same inputs always give the same recommendation, so it is a decision aid rather than an opinion generator.
The rules behind it come from the accuracy evidence rather than preference. Estimates are dependable to about one rep when you are within roughly five reps of failure, and drift beyond two reps of error when many reps remain [3] — which is why the aid pushes you toward percentages when you are stopping far short and do not want to autoregulate.
Accuracy applies to both equally
Because they encode the same judgement, neither escapes the same error. Prediction accuracy differs between single-joint and multi-joint exercises and between trained and untrained lifters [6], and it improves measurably over a few weeks of simply doing it [7].
Does the choice change your results?
Probably not by itself. Training to failure carries at most a trivial hypertrophy advantage over stopping short [4], and strength gain is largely unaffected by how close sets are taken to failure, with only a small dose-response favouring closer to failure for hypertrophy [5]. Both formats let you land in that range. Consistency is what makes either one informative over months.
How Reppit handles it
Reppit logs effort as an integer 1–10 RPE on the set you just finished, and describes every level in reps left in reserve — so the app speaks RPE while thinking in RIR. Target RPE can also be written into a program's set prescription, which is the autoregulated case: the instruction stays fixed while the weight moves with the day [8].
Is RIR more accurate than RPE?
No. They encode the same judgement, so they inherit the same error — accurate to about a rep near failure, worse further out [3]. Any difference is in which question you answer more consistently.
Which is better for beginners?
Counting reps left is usually the more concrete question when the scale has nothing to anchor to yet, and accuracy improves with practice either way [7]. The decision aid above defaults newer lifters to RIR for that reason.
Can I mix them in one program?
Yes, and many programs do — an RPE cap on a heavy top set, a fixed RIR on the back-off work. Just do not switch formats mid-exercise week to week, or your own history stops being comparable.
Sources
- [1]Novel Resistance Training-Specific Rating of Perceived Exertion Scale Measuring Repetitions in Reserve — Journal of Strength and Conditioning Research, 2016. primarySupports: The RIR-anchored RPE scale and its validation against movement velocity in experienced and novice squatters.
- [2]Application of the Repetitions in Reserve-Based Rating of Perceived Exertion Scale for Resistance Training — Strength and Conditioning Journal, 2016. guidelineSupports: Practical application of the RIR-based RPE scale for prescribing and autoregulating resistance training.
- [3]Accuracy in Estimating Repetitions to Failure During Resistance Exercise — Journal of Strength and Conditioning Research, 2017. primarySupports: Estimation error of roughly one repetition near failure, rising above two repetitions when many reps remain.
- [4]Influence of Resistance Training Proximity-to-Failure on Skeletal Muscle Hypertrophy: A Systematic Review with Meta-analysis — Sports Medicine, 2023. meta-analysisSupports: At most a trivial hypertrophy advantage for training to failure versus stopping short of it.
- [5]Exploring the Dose-Response Relationship Between Estimated Resistance Training Proximity to Failure, Strength Gain, and Muscle Hypertrophy: A Series of Meta-Regressions — Sports Medicine, 2024. meta-analysisSupports: Strength gain largely unaffected by proximity to failure, with a small hypertrophy dose-response favouring closer to failure.
- [6]Accuracy of Predicted Intraset Repetitions in Reserve (RIR) in Single- and Multi-Joint Resistance Exercises Among Trained and Untrained Men and Women — Perceptual and Motor Skills, 2023. primarySupports: Differences in RIR prediction accuracy between exercises and between trained and untrained lifters.
- [7]Changes in Intraset Repetitions in Reserve Prediction Accuracy During Six Weeks of Bench Press Training in Trained Men — Perceptual and Motor Skills, 2023. primarySupports: Improvement in RIR prediction accuracy over six weeks of practice.
- [8]Reppit workout logging: per-set RPE wheel and in-app RPE explainer — Reppit (shipped product behaviour), 2026. product-sourceSupports: Reppit's integer 1-10 RPE wheel, its per-level wording, and the reps-in-reserve framing used in the app.