RIR and RPE: what they are, how to measure the intensity of your sets and how many reps to leave in reserve
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When you think you have two reps left, you often have three: on average, people fall short by almost one rep when estimating how far they are from failure. RIR and RPE measure the effort of each set and adjust the weight to the day. This is how to use them well.
In 2022, Halperin and colleagues reviewed the studies in which people predicted how many reps they had left before failure and then checked. On average, participants fell short by almost one rep: they thought they had fewer left than they did. Accuracy improved close to failure and in sets of 12 reps or fewer, and barely depended on experience.
That is the challenge of training with RIR and RPE: they are the best tools for measuring the effort of a set, but you have to learn to use them. Here is what they mean, how close to failure to go for your goal and how to calibrate yourself.
What RIR and RPE are
RIR (reps in reserve) is the number of reps you had left when you ended the set. If you did 8 and could have done 10, you left 2 in reserve: RIR 2. RPE (rating of perceived exertion) is a scale from 1 to 10. Zourdos and colleagues (2016) adapted it to strength training by making each point equal to reps in reserve: RPE 10 means you could not do another; RPE 9, one more; RPE 8, two more.
| RPE | RIR | How it feels |
|---|---|---|
| 10 | 0 | Failure: another rep will not go up with good technique |
| 9.5 | 0 | No more reps, but you could have used slightly more weight |
| 9 | 1 | One left, and only one |
| 8.5 | 1-2 | Definitely one; maybe two |
| 8 | 2 | Two left |
| 7 | 3 | Three left; speed has not dropped much yet |
| 5-6 | 4-6 | Moderate effort; typical of warm-ups or technique work |
One advantage of this scale is that it checks itself: the same study found that the higher the reported RPE, the slower the bar moved. Slowing down is a reliable sign that you are getting close to failure.
How close to failure to go for your goal
Two meta-analyses answer this. The one by Refalo and colleagues (2023) found no advantage in going to complete muscular failure compared with stopping close to it. The one by Robinson and colleagues (2024), which estimated the RIR of each study, found that hypertrophy improves the closer to failure sets end, whereas strength is gained similarly across a wide range of RIR.
| Situation | Recommended RIR | Why |
|---|---|---|
| Hypertrophy, isolation exercises and machines | 0-2 | Closer to failure, more stimulus, and little risk when you fail |
| Hypertrophy, barbell compounds (squat, deadlift, press) | 1-3 | Failing under a heavy load is risky and very fatiguing |
| Maximal strength | 1-4 | Strength is gained similarly across a wide range of RIR |
| Beginner, first weeks | 2-4 | Learn technique before pushing hard |
| Deload week | 4-5 | Recover without losing the habit or technique |
We go deeper in training to failure: how close to go and in volume versus intensity.
RPE or percentages: which works better
Programming with percentages of your max is precise on paper, but it ignores how you feel on the day: if you slept badly, 80% feels like 85%. In the study by Helms and colleagues (2018), two groups did the same sets and reps for eight weeks: one chose the weight by percentage and the other by RPE. They gained strength and muscle similarly, with a likely slight strength advantage for the RPE group.
Autoregulation: RPE matches the weight to how you actually are. On a good day you go up; on a bad day you go down, without breaking the plan. That is why many programmes use it for the main lifts.
How to learn to estimate your RIR
Since people tend to be off by about one rep, it pays to calibrate:
- Calibrate on safe exercises: every now and then, take the last set of a curl, a machine or a lateral raise to failure and compare it with your estimate.
- Do not calibrate on heavy compounds: no failing on squats or deadlifts without a spotter or safety bars.
- Watch the speed: when a rep clearly slows down, there is usually 1 or fewer left.
- Estimate at the end of the set, not halfway through: accuracy improves near the end.
- Write it down: RIR and reps for each set. The log shows whether to add or drop weight.
How to use RIR to progress
RIR works hand in hand with progressive overload: if the plan calls for 3 × 8 at RIR 2 and you finish all three sets at RIR 3 or 4, the weight is too light and it is time to go up. If you hit RIR 0 on the first set, drop it. Many programmes lower the RIR across a block (for example, from 3 to 1) and finish with a deload week. It is a very practical form of periodization.
Common mistakes
- Confusing fatigue with failure: the burn is not failure; failure is when the rep will not go up.
- Always staying far away: RIR 5 on everything is a long warm-up.
- Always going to failure: more fatigue for a small or zero advantage (Refalo, 2023).
- The same RIR on every exercise: isolation work tolerates getting closer to failure than heavy compounds do.
The Progrevia generator assigns each exercise an RIR that changes with the phase of the block and schedules the deload week. All you have to do is log your sets and follow the plan.
- Halperin I, Malleron T, Har-Nir I, Androulakis-Korakakis P, Wolf M, Fisher J, Steele J. Accuracy in predicting repetitions to task failure in resistance exercise: a scoping review and exploratory meta-analysis. Sports Medicine. 2022;52(2):377-390.
- Zourdos MC, Klemp A, Dolan C, Quiles JM, Schau KA, Jo E, et al. Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. Journal of Strength and Conditioning Research. 2016;30(1):267-275.
- Refalo MC, Helms ER, Trexler ET, Hamilton DL, Fyfe JJ. Influence of resistance training proximity-to-failure on skeletal muscle hypertrophy: a systematic review with meta-analysis. Sports Medicine. 2023;53(3):649-665.
- Robinson ZP, Pelland JC, Remmert JF, Refalo MC, Jukic I, Steele J, Zourdos MC. 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;54(9):2209-2231.
- Helms ER, Byrnes RK, Cooke DM, Haischer MH, Carzoli JP, Johnson TK, et al. RPE vs. percentage 1RM loading in periodized programs matched for sets and repetitions. Frontiers in Physiology. 2018;9:247.
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Frequently asked questions
What does RIR 2 mean?
That you ended the set when you could still have done two more reps with good technique. On the reps-in-reserve-based RPE scale it is equivalent to RPE 8.
What is the difference between RIR and RPE?
RIR counts the reps you had left; RPE is an effort scale from 1 to 10. In the strength version by Zourdos (2016) they are equivalent: RPE 10 is RIR 0, RPE 9 is RIR 1 and RPE 8 is RIR 2.
How many reps should I leave in reserve to build muscle?
Between 0 and 2 on isolation exercises and machines, and between 1 and 3 on barbell compounds. Hypertrophy improves close to failure (Robinson, 2024), but going to total failure gives no clear advantage (Refalo, 2023).
Is estimating RIR reliable?
Fairly, with practice. On average people are off by about one rep, and accuracy improves close to failure and in sets of 12 reps or fewer (Halperin, 2022). Calibrating by taking safe exercises to failure helps.
Is it better to program with RPE or percentages?
In an eight-week study (Helms, 2018) both methods produced similar strength and muscle gains. RPE has the advantage of matching the weight to how you feel each day.
Informational content based on the available scientific evidence: it does not replace advice from a healthcare professional. If you have an injury or a medical condition, or are pregnant, check with one before changing your training or diet.
