Reps in Reserve (RIR) and RPE: What the Scale Means and How Accurate It Is

Reps in reserve (RIR) is the number of good reps you could still have done when you ended a set. Two left in the tank is 2 RIR. On the lifting version of the RPE scale, RPE 10 = 0 RIR (failure), RPE 9 = 1 RIR and RPE 8 = 2 RIR.

That is the whole idea. The rest of this guide covers how to rate a set, how accurate lifters actually are at it, and how to use the numbers without turning your training into homework. It sits inside our wider guide to load, rep ranges, RIR and rest intervals, so think of this page as the vocabulary lesson that everything else builds on.

What do reps in reserve and RPE actually mean?

RPE stands for rating of perceived exertion. The classic version is a general 1-10 “how hard was that?” score, which is vague. The lifting-specific version ties each number to a count of reps left, so a “9” means something concrete.

That version was proposed by Zourdos and colleagues in 2016, who set RPE 10 = 0 RIR, RPE 9 = 1 RIR “and so forth” (Zourdos et al., 2016). A companion paper by Helms and colleagues explained how to build the scale into a training plan, noting that it adjusts loads to match the lifter from set to set and may gauge intensity more precisely near the limit (Helms et al., 2016).

So what is the difference between RIR and RPE? Mostly wording. RPE is a score, RIR is a count. If you like numbers on a 10-point scale, say RPE 8. If you prefer thinking in reps, say 2 RIR. A free RIR and RPE calculator on this site converts between the two if you want a quick check.

How do you calculate RIR in the gym?

You do not calculate it. You estimate it, and the estimate has to be honest about what counts as a rep. A grinding rep with your hips shooting up is not a good rep. A rep that is slow but looks like the previous ones is.

A simple way to rate a set:

1. Finish the set at the rep count you planned.
2. Ask: could I have done one more with the same form? If clearly yes, ask again for a second.
3. Stop counting when you honestly say “no” or “maybe, but it would be ugly”.
4. Write the number down next to the weight and reps.

That last step matters more than it looks. A log of “80 kg x 9 @ 2 RIR” gives you something to compare with next week. Without it, RIR becomes a mood.

Does the RPE scale line up with real effort?

There is decent support for the idea that the scale tracks something measurable. Bar speed drops as sets get harder, and ratings drop with it.

In the original 2016 study of 29 people (15 experienced and 14 novice squatters), there was a strong inverse relationship between average bar velocity and RPE across intensities (r = -0.88 in experienced lifters and r = -0.77 in novices) (Zourdos et al., 2016). A bench press study of 27 college-aged men found strong inverse correlations between bar speed and RPE in both experienced and novice groups (reported as r = 0.85 each), and the authors concluded the scale may work for autoregulating bench press load and volume in that population (Ormsbee et al., 2019).

Both studies were small, short, and used young adults, and the lifting version of the scale was developed by the same research group. A broader 2025 systematic review of 18 studies reported moderate positive correlations among RPE scales, movement velocity and training load, and concluded RPE can serve as a practical, low-cost way to monitor training load (Petro et al., 2025). Its authors also say that training level, motivation and environmental conditions can affect perceived exertion.

One more detail worth knowing: experienced squatters and benchers rated a max single higher than novices did, which hints that experience changes how you read the scale at the extremes (Zourdos et al., 2016); (Ormsbee et al., 2019).

How accurately can lifters judge reps in reserve?

Better than most people assume, with caveats.

In a 2024 study, 24 resistance-trained men and women (12 each) did bench press sets to failure at 75% of 1RM, and said “stop” when they felt they hit either 1 RIR or 3 RIR. The average error was small: -0.17 reps in direction and 0.65 reps in absolute size. Accuracy did not differ between 1 RIR and 3 RIR guesses, and the researchers found no link with sex, years of training or relative strength (Refalo et al., 2024).

On machine-based single-joint moves, a 2023 study of 27 men and 31 women (trained and untrained) found guesses were more accurate when closer to failure and in later sets, while sex and training experience did not significantly change the error (Remmert et al., 2023).

So what is the catch? Distance from failure. If you are guessing at 5 reps left, you have more room to be wrong than at 1 rep left. A 2024 scoping review of 31 studies suggested that RIR predictions should be made close to task failure to improve accuracy (Bastos et al., 2024).

Where the evidence is weaker

Not every group does as well. In a 2025 trial of 25 community-dwelling older adults (average age 68), predicted RIR on chest press at 65% of 1RM was off. The authors report that participants underestimated the number of reps by about 2.1 at a predicted 2 RIR and 1.6 at 4 RIR, though not at 6 RIR. RPE barely moved across those sets (8.0, 7.6 and 7.3). The authors concluded RIR may lack precision for prescribing load in this group but could be useful for volume monitoring alongside RPE (Gomez-Redondo et al., 2025).

Why do the results differ from the trained-lifter studies? Different people, different exercise, a different load and a different method for locating “predicted” RIR. It is not a clean head-to-head. The practical read: RIR is usable, but the less experience you have with an exercise, and the further from failure you are guessing, the more padding you should leave. For a deeper dive, see our article on how accurately lifters gauge RIR and failure.

How do I use RIR to autoregulate my training?

Autoregulation just means adjusting the work based on how you are doing today. A fixed percentage of your max cannot know you slept five hours or that it is 38 degrees in a gym without AC. Your read on a set can.

A simple pattern for an upper-body press:

• Target: 8-10 reps at about 2 RIR.
• Set 1: 70 kg for 10 felt like 4 RIR. Too easy. Add weight.
• Set 2: 77.5 kg for 9 felt like 2 RIR. On target. Repeat.
• Set 3: 77.5 kg for 8 felt like 1 RIR. Fine, but do not add weight yet.

That is an example, not a prescription. Your numbers will differ. The point is that the load follows the target instead of the other way round. For a structured version of this, see autoregulated progressive overload (APRE) rules.

For heavy powerlifting-style work, many lifters use the same scale for top singles and back-off sets, covered in RPE-based powerlifting.

What RPE or RIR should I aim for on warm-ups and working sets?

Warm-ups are not rated, since their job is to get you ready rather than to train you. Ramp up so the last warm-up feels fast and light, then start rating your working sets. Our guide to warm-up ramping without fatigue shows a simple way to do it.

For working sets, here is a practical starting map. It is a coaching guideline, not a research-derived prescription.

Situation	Typical RIR target	RPE
Learning a new exercise	3-4	6-7
Most compound working sets	2-3	7-8
Most isolation and machine sets	1-2	8-9
Last set of an exercise, safe machine or cable	0-1	9-10

Whether closer to failure builds more muscle is a separate question that depends on the study and on volume. That is covered in training to failure versus RIR for hypertrophy, so we will not rehash it here. For this page, the point is that you need the language before you can pick a target.

How do I get better at judging RIR?

Accuracy is a skill, and the research suggests practice and closeness to failure both help.

• Use the same exercises for a while. You learn the feel of a lift by repeating it.
• Check against reality now and then. On a cable or machine exercise, stop where you think you have 2 left, rest a minute, and then see how many reps you actually get. That is your error, measured.
• Watch the bar. Compare your last rep’s speed to your first rep.
• Lean cautious early on. If you are unsure whether you have 3 left or 5, assume fewer.
• Do not chase certainty. Even trained lifters miss by a rep on average, so use the number as a guide, not a measurement.

A fuller protocol is in our piece on calibrating true RIR with gym protocols.

What should you remember about reps in reserve?

Reps in reserve is a simple count of the reps you had left, and RPE is the same idea on a 10-point scale. The research supports it as a practical tool for trained lifters, particularly on familiar exercises and close to failure, and it is less precise for beginners, for older adults, and when you are guessing from far away.

Pick a target, rate your sets honestly, log it, and let the numbers nudge your load. If you want a starting plan that uses these ideas, our free workout plans are a place to begin.