RPE and RIR: What They Mean and How to Use Them
RPE 8 means you could have done two more reps. That is the whole concept — but it leads to a way of adjusting load to the day that a fixed percentage program cannot do.
The program says "3 × 5 @ RPE 8". No percentage, no load. The idea is that the lifter picks the weight based on how the set feels.
That sounds vague next to "3 × 5 @ 82.5 %". In practice it is often more accurate, and the reason is simple: the percentage is derived from a number measured at some point in the past, while RPE is measured today.
Two numbers, one idea
RIR stands for reps in reserve. It is as direct as it sounds: if you could have done two more reps after the set, RIR is 2.
RPE stands for rate of perceived exertion. The scale used in strength training runs 1–10 and is defined specifically in terms of reps left in the tank. So the two are directly linked:
RIR = 10 − RPE
They are the same information expressed two ways. RPE 8 and RIR 2 mean exactly the same thing. Which one you use is a matter of taste — some programs speak one language, some the other.
An aside: the original RPE scale dates from around 1970, was built for endurance work, and runs from 6 to 20. The 1–10 strength scale is a different thing that borrowed the name. If you meet a scale with two-digit numbers, it is the other one.
The scale
| RPE | RIR | What it feels like |
|---|---|---|
| 10 | 0 | Not one more rep was available. |
| 9.5 | 0–1 | A second rep might not have gone up. |
| 9 | 1 | One more rep, certainly. |
| 8.5 | 1–2 | One for sure, maybe two. |
| 8 | 2 | Two more reps were there. |
| 7 | 3 | Three in reserve. Heavy but controlled. |
| 6 or below | 4+ | Warm-up or technique work. |
The half-point steps are not fussiness. The gap between RPE 9 and 10 is larger than the gap between 7 and 8, because the top of the scale is compressed: the last reps cost more than the first ones. That is exactly where the halves earn their place.
How RPE converts to a percentage
This is the heart of the conversion, and it is simpler than it looks. A set at RPE X is the same load as a rep max that includes the reps you left behind.
Three reps at RPE 8 means two more were available. So the load is one you could have got five reps with — a five-rep max. And a five-rep max is famously around 87 % of a one-rep max.
You can verify this in the RPE chart: three reps at RPE 8 and five reps at RPE 10 both give 86.8 %. They are the same load, because they are the same load.
| Reps | RPE 10 | RPE 9 | RPE 8 | RPE 7 |
|---|---|---|---|---|
| 1 | 100.0 % | 94.9 % | 91.9 % | 89.3 % |
| 2 | 94.9 % | 91.9 % | 89.3 % | 86.8 % |
| 3 | 91.9 % | 89.3 % | 86.8 % | 84.6 % |
| 5 | 86.8 % | 84.6 % | 82.5 % | 80.4 % |
| 8 | 80.4 % | 78.5 % | 76.7 % | 74.9 % |
Every row shows the same pattern: one step down the RPE scale is worth roughly one extra rep. That is not a coincidence — it is the principle the chart is built on.
On this site the RPE chart and the percentage chart come from the same model as the 1RM calculator. That is deliberate: three calculators should give one answer to one situation, otherwise they are just three opinions.
Why lifters use RPE
A fixed percentage assumes your max is a constant. It is not. The same lifter is in different shape on different days, and the spread is wider than most people assume — sleep, food, stress and the residue of the last session move daily capacity by several percent either way.
When a program says 85 %, it says the same number on a bad day and a good one. On the bad day it is too much, and the set fails or the technique does. On the good day it is too little, and the stimulus is left on the table.
RPE inverts this. The program prescribes the effort, and the load follows the day. On a bad day RPE 8 means a lighter bar, on a good day a heavier one — and in both cases the session lands where it was meant to land.
There is a practical benefit too: RPE works without a recent max test. You do not need a number you have not measured, and you are not forced to test a max just to give the program a starting point. And once you do have an estimate, the strength standards turn it into something comparable: what level that lift sits at for your bodyweight.
Where RPE breaks down
This is the part usually left out.
The estimate requires experience of failure. You cannot know what one rep in reserve feels like if you have never been in the situation where there were none. A lifter who has never taken a set to the end underrates their own RPE systematically. In practice this means a lot of people call a set RPE 8 when it was really 9.5.
Beginners cannot rate accurately. In the first months technique and strength change quickly and the feel has not had time to calibrate. Fixed loads and straight session-to-session increases work better then.
Accuracy collapses at high reps. RPE is at its most reliable in sets of one to five. In a set of ten or fifteen, fatigue and discomfort pile up to the point where telling two reps in reserve from four is genuinely hard. The same misjudgement up there also means many more actual reps and considerably more accumulated fatigue.
Lifts differ. The usual coaching observation is that deadlift reps slow visibly near the end, making reps in reserve easy to sense, while the difference between one and two is subtler on the bench. The research on between-lift differences is mixed, though, so treat this as an experience-based rule rather than a measured finding.
Calibrating your estimate
RPE is a skill, not a trait, and it can be trained.
- Go to genuine failure occasionally. Take an accessory lift — not a squat or deadlift, something safe — to true failure once a month. It gives you the reference point that the top of the scale is guesswork without.
- Guess before you lift. Write down the RPE you expect before the set and the RPE you got after it. The gap between those two is the thing you are learning.
- Check it against the calculator. Put the set into the RPE chart and see what max it implies. If that number swings by tens of kilos week to week, your estimate is not stable yet.
- Use bar speed as a cue. A visible slowdown is a more reliable signal than a feeling. If the third rep moves as fast as the first, the set was nowhere near RPE 9.
Using both together
You do not have to choose between RPE and percentages. The most common workable model uses both:
- Top set by RPE. Work up to the day's heaviest set by feel — say one set of three at RPE 8. This set measures the day.
- Back-off sets as a percentage of that. Calculate the remaining work from the top set, for example 85–90 % of it. The whole session then scales with the day while the structure stays predictable.
This is the same idea as the AMRAP set in 5/3/1: one set tells you where you are, and the rest of the program leans on that information without ever testing a max.
Summary
RPE 8 means two reps in reserve, and RIR = 10 − RPE. The conversion to a percentage works because a set at RPE X matches a rep max that counts the leftover reps — three reps at RPE 8 is the same load as a five-rep max.
RPE is most useful for an experienced lifter at low reps, and least reliable for a beginner at high reps. It does not replace percentages; it complements them. The percentage says what the program planned, the RPE says what today is offering.
Conversions in both directions are in the RPE chart.