Rate of Perceived Exertion and Reps in Reserve, Explained
Reps in reserve (RIR) is the number of good reps you could still have done when you stopped a set. Rate of perceived exertion (RPE), in the version used for lifting, is the same idea on a 1 to 10 scale: RPE 10 means you could not have done another rep, RPE 9 means one left, RPE 8 means two left. So a set at RPE 8 is a set finished with two reps in reserve. Most productive strength work for healthy adults sits around RPE 7 to 9, or one to three reps in reserve.
That is the whole concept. The skill is in rating sets honestly and using the numbers to make decisions, which is what the rest of this piece covers.
Where the two scales come from
The original rating of perceived exertion was developed by the Swedish psychologist Gunnar Borg for whole-body effort, such as cycling or running, and is still used in cardiac rehabilitation and endurance training. It asks how hard the work feels overall.
That kind of scale is not much use for a set of eight squats, because almost any hard set feels “very hard” by the end. Strength coaches adapted it so that each number on the 1 to 10 scale is anchored to a concrete question: how many more reps could you have done? That is the RIR-based RPE scale most lifters now use, and it is the one that matters in the gym.
The scale in practice
| RPE | Reps in reserve | What it feels like |
|---|---|---|
| 10 | 0 | Could not have done another rep with good form |
| 9 | 1 | One more was possible, and it would have been a grind |
| 8 | 2 | Last rep slowed noticeably, two more were there |
| 7 | 3 | Bar speed still decent, clearly hard but controlled |
| 5 to 6 | 4 or more | Warm-up territory, or deliberate technique work |
You will sometimes see half points, such as RPE 8.5, meaning you might have managed one more rep, or might have needed to add a little weight. Beginners do not need them.
Why bother with it at all
A programme that says “3 sets of 8 at 60kg” assumes you are the same person every week. You are not. After a bad night’s sleep, a long-haul flight or a stressful week at work, 60kg can feel very different. RPE lets the plan flex with you. “3 sets of 8 at RPE 8” means you choose the weight that gives you two reps in reserve on that day. On a good day it might be 62.5kg, on a rough day 57.5kg. The effort, which is what actually drives adaptation, stays where it should be.
Coaches call this autoregulation. It is particularly useful for busy adults whose recovery is shaped by things outside the gym, and it pairs naturally with progressive overload, because you can see the weight at a given RPE climb over the weeks.
How to rate a set honestly
The catch is that most people are poor judges of their own reps in reserve at first. Studies of lifters’ estimates have generally found that less experienced trainees tend to underestimate how many reps they have left, particularly on higher-rep sets. In plain terms: a set that feels like RPE 9 is often closer to RPE 7.
Some ways to calibrate:
- Rate the set immediately, before you rack the weight or put the dumbbells down. Your judgement gets kinder within seconds.
- Use bar speed as a cue. When the last rep is clearly slower than the first, you are usually within two or three reps of failure.
- Test occasionally on safe exercises. On a machine, a leg press or a dumbbell exercise, take one set to genuine failure and compare it with what you predicted. Do this sparingly, and not on heavy barbell squats without a spotter or safety arms.
- Write it down. Log the weight, reps and the RPE you gave it. Over a few weeks, patterns appear.
- Get a second opinion. A coach watching from the side sees things you cannot feel, such as the rep where your form started to change.
How hard should most sets be?
For most healthy adults whose goal is strength, muscle and general fitness, a sensible default looks like this:
- Main compound lifts (squat, deadlift variations, presses): RPE 7 to 8. These are the exercises where fatigue affects technique most and where a missed rep carries more risk.
- Accessory and machine work (rows, pulldowns, cable work, lunges): RPE 8 to 9, occasionally 10 on the last set of a safe exercise.
- Warm-up sets: RPE 5 or below. Their job is to prepare you, not tire you.
Training to true failure on every set is not necessary for good results and makes recovery harder, especially across a week with three or four sessions. Stopping one to three reps short gets you most of the benefit for less fatigue. Our guide on how many sets and reps to build muscle goes into how effort and volume interact.
Using RPE to adjust a session
Once you can rate sets reasonably well, RPE becomes a simple decision tool:
- Target RPE 8 and the first set felt like 6? Add weight for the next set.
- First set already at 9.5? Take a little off. You will get better quality reps and a better session.
- Same weight feeling a full point harder for two or three sessions in a row? That is often a sign you need an easier week. See our piece on the deload week.
- Same weight feeling a point easier than last month? You have got stronger. Move the weight up.
Common mistakes
- Counting reps with poor form as “reserve”. Reps in reserve means good reps. If your back would round or your hips would shoot up, those reps do not count.
- Rating every set as an 8. If your log only ever says 8, you are not really rating.
- Using RPE as an excuse. Autoregulation can drift into always choosing the easy option. The numbers should still go up over months.
- Applying it to everything. RPE works best for sets of roughly 3 to 12 reps. For very high reps it gets much harder to judge.
In the studio, every session is logged with weights, reps and effort, so you build up an honest record of what each number actually feels like for you. If you would like that kind of coaching in a private room, here is how 1-1 training in Highgate works.
If you have high blood pressure, a heart condition or a recent injury, or are pregnant, speak to your GP before training close to failure. The NHS strength exercise pages are a sensible place to start if you are new to it.
Questions we get asked
Is RPE 8 the same as two reps in reserve?
Yes, on the lifting version of the scale. RPE 8 means you stopped with roughly two good reps left.
Should beginners use RPE?
Yes, but loosely, ideally with a personal trainer checking your ratings at first. Aim for sets that feel hard while form stays clean, roughly RPE 7, and expect your ratings to get more accurate over the first few months.
Do I ever need to train to failure?
Not routinely. Occasional sets to failure on safe exercises help calibrate your ratings, but most of your training can stop one to three reps short.
Is RPE the same as the Borg scale used in cardio?
They share a name and a history, but the lifting version is anchored to reps in reserve, so the numbers mean something more specific.
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