Knowledge base/Training basics
What is RIR, and how do you estimate it?
In short
RIR stands for reps in reserve. It is the number of reps you could still have done when you ended a set. If you stop at 8 reps and could have done 10, you had 2 in reserve (RIR 2). Most people guess within a rep or two when the set is close to failure, and further off when it is not.
Cody de LeeuwLast checked 27 October 2026 · 6 min read
What does RIR mean?
RIR is short for reps in reserve. When a set ends, you ask: how many more clean reps could I have done? That number is your RIR.
- RIR 0: nothing left. The next rep would not have gone up.
- RIR 1: one more rep, with effort.
- RIR 2: two more reps.
- RIR 3 or more: the set felt easy.
The scale comes from strength training research. Zourdos and colleagues linked it to the 1 to 10 effort scale many lifters know: RPE 10 is 0 reps in reserve, RPE 9 is 1, RPE 8 is 2, and so on.1 A set that ends at RIR 2 is the same as an RPE 8. RIR vs RPE goes into the difference.
How do you estimate it?
Count after the set, not during it. When you rack the weight, think about the last rep and ask what the next one would have looked like.
- Bar speed. If the last rep was about as fast as your first, you had plenty left. If it crawled and your form started to slip, you had 0 or 1.
- Form. A rep you could only finish by changing your technique does not count as a rep you had in reserve.
- Honest count. Be strict. “I could probably squeeze one more” is RIR 1, not RIR 3.
Bar speed is a real signal. In a study of 29 squatters, the slower the bar moved, the higher the lifters rated the effort. The link was strong in both experienced lifters and novices.1
Judging a set that ended with 5 reps left is hard. Judging one that ended with 1 left is much easier. So use RIR mostly to tell hard sets from easy ones, and do not worry about telling RIR 4 from RIR 5.
How accurate are people?
Not perfect, but usable. Researchers have people predict how many reps they have left, then make them go to failure to check.
| Study | People | What it found |
|---|---|---|
| Hackett 20173 | 81 adults, chest press and leg press | Error of about 1 rep when 0 to 5 reps from failure. More than 2 reps when 7 to 10 reps from failure. |
| Steele 20175 | 141 people, full body session | People underpredicted how many reps they could do. The typical error was 2.6 to 3.4 reps. There was a tendency to do better with more experience. |
| Halperin 20224 | 12 studies, 414 people | On average people underpredicted by about 1 rep, with large differences between studies. Training status made no clear difference. |
Three patterns repeat. People tend to guess that they have fewer reps left than they really do. Guesses are better close to failure, with heavier weights (12 reps or fewer), and in later sets.4 And the studies disagree on whether experienced lifters do better, so do not assume you are good at it or bad at it.
The practical point: an RIR of 2 is really “somewhere around 1 to 3”. Treat it as a rough guide, not a measurement.
How do you use RIR to choose the weight?
The idea is to adjust the load from set to set, based on how hard the last set felt.2 You pick a target RIR for the exercise, say 2, then compare.
| Target | You logged | Next set |
|---|---|---|
| 8 reps at RIR 2 | 80 kg × 8, RIR 3 or more | Heavier: 82.5 kg, around 7 reps |
| 8 reps at RIR 2 | 80 kg × 8, RIR 2 | Stay: 80 kg |
| 8 reps at RIR 2 | 80 kg × 8, RIR 0 | Same weight, aim for 6 reps |
Across weeks, the same logic tells you when to add weight. If every set at the top of your rep range felt like RIR 3, the weight was too light. If you hit the top of the range but only just, you earned the increase. Double progression uses exactly this.
Why stop a rep or two short of failure?
Most of your sets do not need to be all-out. A meta-analysis of 15 studies found no evidence that training to momentary failure beats stopping short of it for muscle growth. Sets taken to any kind of failure had a small edge overall (effect size 0.19), and the authors suggest the link between closeness to failure and growth is not a straight line.6
Stopping at RIR 1 to 3 has practical benefits. You can count your reps honestly, your technique stays clean, and you are ready for the next set. It also builds in some room for the estimation error above: if you aim for 2 and are off by one, you still end the set short of failure.
That is a habit more than a rule. A last set on a leg extension taken to failure is fine. A heavy deadlift taken to failure is a worse bet, because a missed rep costs more. Do you need to train to failure? covers when each makes sense.
Moderate evidence
The RIR scale was checked against bar speed in one small study, and several studies have measured how well people predict their reps to failure. Using RIR to pick weights is coaching practice. How we rate evidence
How Mitta does it
RIR, logged in one tap.
After a set you can tell Mitta how many reps you had left. Mitta uses that number to adjust your next set and your next target, and it shows you the reason.
- One tap per setChoose 0, 1, 2 or 3+ reps left. Beginners see Easy, Good and Hard instead, saved as 3, 2 and 1.
- The next set adjustsFelt easy (3 or more left, above your target): a step heavier. Far harder than planned: same weight, fewer reps, or a step lighter. On target: no change. No change if you flagged pain.
- A target per exerciseWorking sets aim 1 to 3 reps short of failure, and at least 2 on heavy barbell lifts. In a training block the target drops week by week.
- Counted in your estimated 1RMReps left count towards the estimate, up to 4, because guesses beyond that are unreliable.
Stop guessing between sets.
Tell Mitta how the set felt and it adjusts the next one. Free to start, in the web app for invited testers.
Questions about
RIR, and how do you estimate it
Is RIR the same as RPE?
They describe the same effort from two sides. RIR counts the reps you had left. RPE is a 1 to 10 rating. RPE 10 is RIR 0, RPE 9 is RIR 1, RPE 8 is RIR 2.
What if I have no idea how many I had left?
Start with three answers: easy, good, or hard. Easy is about 3 or more left, good is about 2, hard is about 1. Sharper numbers come with practice. Doing a few sets to failure on safe exercises, like a machine, can calibrate your sense.
Do warm-up sets get an RIR?
No. RIR is for working sets, the ones that are meant to be hard.
Does RIR work for high-rep sets?
Less well. Studies find the guess is worse when a set goes past about 12 reps. For sets of 15 or 20, tiredness and burning make it hard to judge what is left.
Should I log RIR on every set?
It helps most on the last set of each exercise, where the effort is highest. Logging it every set gives the best picture, but a rough number on the last set is already useful.
Sources
- Zourdos MC, Klemp A, Dolan C, 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. doi.org/10.1519/JSC.0000000000001049
- Helms ER, Cronin J, Storey A, Zourdos MC. Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength & Conditioning Journal, 2016; 38(4): 42–49. doi.org/10.1519/SSC.0000000000000218
- Hackett DA, Cobley SP, Davies TB, Michael SW, Halaki M. Accuracy in estimating repetitions to failure during resistance exercise. Journal of Strength and Conditioning Research, 2017; 31(8): 2162–2168. doi.org/10.1519/JSC.0000000000001683
- Halperin I, Malleron T, Har-Nir I, et al. Accuracy in predicting repetitions to task failure in resistance exercise: a scoping review and exploratory meta-analysis. Sports Medicine, 2022; 52(2): 377–390. doi.org/10.1007/s40279-021-01559-x
- Steele J, Endres A, Fisher J, Gentil P. Ability to predict repetitions to momentary failure is not perfectly accurate, though improves with resistance training experience. PeerJ, 2017; 5: e4105. doi.org/10.7717/peerj.4105
- 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. doi.org/10.1007/s40279-022-01784-y
Written by Cody de Leeuw. First published 27 October 2026, last checked 27 October 2026. This article is general information, not medical advice. Spotted a mistake? Tell me