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RPE and RIR: measuring how hard a set was

RPE, the rating of perceived exertion, scores how hard a set was on a scale of 1 to 10. RIR, reps in reserve, counts how many more reps you could have done. In lifting they are two views of the same thing: RPE 10 is zero reps left, RPE 9 is one, RPE 8 is two.

This reps-in-reserve version of RPE comes from a 2016 study by Zourdos and colleagues. Across 29 people squatting, the ratings tracked bar speed closely: the slower the rep, the higher the RPE (Zourdos et al., 2016). Helms, Zourdos and colleagues later described how to use the scale to plan training (Helms et al., 2016).

Both let a plan prescribe effort instead of a fixed weight, and effort adapts by itself to good days and bad ones.

The scale

The version used in strength training, set out by Zourdos and colleagues in 2016 as an adaptation of an older scale from endurance sport, ties each score to reps in reserve:

  • RPE 10, 0 RIR: maximal. No more reps, and no more weight.
  • RPE 9, 1 RIR: one more rep was possible.
  • RPE 8, 2 RIR: two more. A common target for working sets.
  • RPE 7, 3 RIR: three more. Hard, with a clear margin.
  • RPE 6 or lower, 4 or more RIR: moderate. Useful for technique work and warm-ups.

Why it beats a fixed number

A plan that says “5 reps at 100 kg” assumes you are the same person every day. You are not: sleep, stress, food and last week’s training all move your strength by a few percent. “5 reps at RPE 8” asks you to find the weight that is right today.

It also guards against the two classic mistakes: every set to failure, which piles up fatigue, and every set comfortably easy, which does not drive progress.

Everyone guesses low at first

Beginners usually underestimate how many reps they have left, often by several. A set that feels like the limit is frequently two or three reps from true failure. Accuracy improves with practice, and is better on sets with fewer reps.

A simple way to calibrate: on the last set of a safe exercise, such as a machine or a dumbbell curl, predict your RIR, then keep going to failure. The gap between the guess and the result is your correction.

How hard should most sets be?

For building muscle and strength, most working sets land well at about 1 to 3 reps in reserve. Going to failure now and then, on safe exercises, is fine and useful for calibration. On heavy squats and deadlifts it adds a lot of fatigue and risk for little extra benefit.

Wherever you log your training, note how many reps you had left next to the weight and reps. It makes choosing next week’s weight far easier.

Updated

Sources

  1. Zourdos MC, Klemp A, Dolan C, et al. (2016). Novel Resistance Training-Specific Rating of Perceived Exertion Scale Measuring Repetitions in Reserve. Journal of Strength and Conditioning Research.
  2. Helms ER, Cronin J, Storey A, Zourdos MC (2016). Application of the Repetitions in Reserve-Based Rating of Perceived Exertion Scale for Resistance Training. Strength and Conditioning Journal.

FAQ

Frequently asked questions

Is RPE the same as RIR?

Nearly. In lifting, RPE is usually defined through reps in reserve, so RPE 8 equals 2 RIR. RPE also covers sets where reps are not the limit, such as a heavy single, where you judge whether more weight was possible.

Should beginners use RPE?

It helps to learn the idea early, but expect your ratings to be off for a few months. Many beginners do well on simple progression first, adding weight or reps each week, and bring in RPE once their judgement improves.

Can I use RPE for cardio?

Yes, that is where the idea began. For running or cycling it rates overall effort rather than reps left.

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