Training
RPE and RIR: the two ways to say how hard a set was
Two scales, one idea: how close to failure you stopped. Here is the table that joins them, and what the numbers do the next day.
What do RPE and RIR mean?
RPE, rating of perceived exertion, scores a set from 1 to 10, where 10 means no further rep was possible. RIR, reps in reserve, counts the reps you could still have done: RIR 0 is failure, RIR 2 means two more were in the tank. For strength training the two are mirror images of each other — RPE 8 is RIR 2, RPE 9 is RIR 1 — and the RIR-based version was formalised for lifting by Zourdos and colleagues in the Journal of Strength and Conditioning Research in 2016.
Both exist because “how heavy” is not the same as “how hard”. The same 100 kg is RPE 6 on a fresh day and RPE 9 after four hours of sleep, and only the second number tells the coach anything. Neither replaces the weight on the bar; they describe the effort the weight cost, which is the part that changes from one day to the next.
How do RPE and RIR map to each other?
| RPE | RIR | Means |
|---|---|---|
| 10 | 0 | No further rep was possible |
| 9 | 1 | One more rep, possibly |
| 8 | 2 | Two more reps, clearly |
| 7 | 3 | Three more; bar speed still good |
| 6 and under | 4+ | Warm-up territory |
Most working sets for strength and muscle live between RPE 7 and 9. Sets to RPE 10 have a place, mostly on the last set of an isolation exercise; they are expensive on a squat.
How does Liftor use the numbers?
As the gate on progression. When you log a set with its reps in reserve, Liftor suggests more weight next time only if the top set finished with at least two reps in reserve — RPE 8 or easier. A top set at RIR 1 or 0 holds the weight and asks for the reps again, which is how a progression stays a progression rather than a sequence of grinders. The same reserve feeds the estimated one-rep max the Strength Score reads, so an honest RIR makes every number in the app more accurate. A generous one makes them worse, and the app finds out on the next set anyway.
How does RPE map to a percentage of your one-rep max?
Through the reps you could have done. A set of five at RPE 8 had two in reserve, so it was really a set of seven to failure, and seven reps to failure is about 81% of a one-rep max on the Epley curve — 1 ÷ (1 + 7 ÷ 30). Add the reps done to the reps in reserve, and the table gives the load:
| Reps done | RPE | Reps to failure | About % of 1RM |
|---|---|---|---|
| 1 | 10 | 1 | 100% |
| 3 | 8 | 5 | 86% |
| 5 | 10 | 5 | 86% |
| 5 | 9 | 6 | 83% |
| 5 | 8 | 7 | 81% |
| 8 | 8 | 10 | 75% |
| 10 | 8 | 12 | 71% |
The numbers are the Epley formula run backwards, and they carry its limits: past about twelve reps to failure the curve flattens and the percentages stop meaning much. Which is also why Liftor caps its one-rep max estimates at twelve reps.
How accurate are RPE ratings?
Accurate enough to train by, and more accurate the closer you get to failure. Zourdos and colleagues validated the reps-in-reserve scale against bar speed in 2016: as lifters’ ratings rose toward ten, the bar measurably slowed, and the inverse relationship held in both groups — tighter in the experienced squatters than in the novices — with the experienced lifters also reporting a higher RPE at their true max, which the authors read as greater efficiency at the top end. The ratings drift most on easy sets, where nobody can tell RPE 5 from RPE 6, and least on the sets that decide anything.
Two habits fix most of the drift. Rate the set within a few seconds of racking it, before the story about it forms. And rate the last rep, not the set: RIR is a question about how many more, and the honest answer is usually one fewer than the first number that comes to mind. Liftor stores what you log, and the estimated max it derives will tell you within a week whether your eights were really eights.
How do you use RPE to pick a weight?
Start from the prescription and adjust by feel, in steps of about five percent. A set written as five reps at RPE 8 wants a load that leaves two in the tank; warm up, take a working guess, and if the first set was RPE 6 add five percent for the next, if it was RPE 10 take five percent off. Helms and colleagues laid out this application of the scale in 2016, and it is how most auto-regulated programmes are run: the reps and the target effort are fixed, the load floats to meet them, and a bad day produces a lighter bar instead of a missed set.
Liftor writes the load for you and reads your RIR back to check it. A top set logged at RIR 2 or more is a green light for the next step; RIR 1 holds; RIR 0 holds and usually earns a note. The rest timer adds fifteen seconds when the load is at or above 85% of your best on that lift, because sets that heavy are decided by recovery between them as much as by effort within them.
Sources
- Zourdos MC 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
- Helms ER, Cronin J, Storey A, Zourdos MC. Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength and Conditioning Journal, 2016; 38(4): 42–49
- Epley B. Poundage chart. Boyd Epley Workout. Lincoln, Nebraska: Body Enterprises, 1985 — the formula the percentage table below is derived from
- Liftor’s progression gate: two reps in reserve on the top set before the load rises (utils/progressiveOverload.ts)