RIR vs RPE: Differences, Conversion Chart and When to Use Each

For a set of weights, RIR and RPE measure the same thing, how close to failure you finished, just counted in opposite directions. RPE (rating of perceived exertion) climbs to 10, which is failure; RIR (reps in reserve) counts down to 0, which is also failure. So RIR = 10 − RPE: an RPE 8 set is an RIR 2 set.

If you're not sure what RIR is yet, start with what RIR is and how to use it. This article is about RPE: where it came from, the full conversion chart, when each one makes sense, and what to make of the RPE load charts you'll find online.

Where RPE comes from: from Borg to the barbell

RPE wasn't invented for the gym. The original scale was created by Swedish researcher Gunnar Borg and used mostly for aerobic exercise: it ran from 6 to 20 to roughly match heart rate. Borg later presented a method that combines categories with ratio properties (Borg, 1982), which gave rise to the CR10 scale, the first to rate exertion from 1 to 10. The OMNI scale, also 1–10 and illustrated with pictures, came after.

Lifters used these scales for years, but there was a catch: studies kept finding that people gave less-than-maximal ratings even when they had just done every rep they could with that weight (Helms et al., 2016). "About an 8 out of 10" didn't tell a coach how far the lifter was from failure.

The fix was to tie each number to something you can count: reps left. In 2016, Zourdos and colleagues published a resistance-training RPE scale where RPE 10 means zero reps in reserve, RPE 9 means one, and so on (Zourdos et al., 2016). According to Helms and colleagues, a scale like this was already in use in powerlifting, in the 2008 Reactive Training Systems manual; Zourdos' work brought it into the research literature.

When a strength program says RPE today, it almost always means this version, not Borg's.

Full RPE to RIR chart

RPE	RIR	What it means
10	0	Max effort: not one more rep
9.5	0–1	Maybe one more, maybe not
9	1	One rep left
8.5	1–2	One left for sure, maybe two
8	2	Two reps left
7.5	2–3	Two left for sure, maybe three
7	3	Three reps left
5–6	4–6	Moderate set
3–4	—	Light effort
1–2	—	Little to no effort

Two notes on this chart:

• The whole numbers come from the published scale (Zourdos et al., 2016). Below RPE 7 it stops counting reps: RPE 5–6 covers 4 to 6 reps in reserve, and RPE 1–4 is described only as light or minimal effort. The reasoning, per Helms et al. (2016), is that far from failure people can't judge precisely and a range is easier to give.
• Half points (9.5, 8.5, 7.5) are a coaching convention, not part of that scale. They're there for when you can't decide between two values. They do appear, for example, in the load chart Helms et al. (2016) published, covered below.

RIR vs RPE: the practical differences

If they measure the same thing, what's actually different? How you use them:

	RPE	RIR
What you report	An effort rating from 1 to 10	Reps you had left
Failure	10	0
Easy efforts	Has ratings for them (1–6)	Loses precision past 4–5 reps
Most common in	Powerlifting and strength programs	Hypertrophy training and workout apps
For beginners	Less intuitive at first	"Two left" explains itself

Neither is more accurate. On the reps-in-reserve scale, RPE 8 and RIR 2 are literally the same set. Accuracy depends on how well you estimate, not on what you call the number.

When to use each

This is practical judgment, not something the research has compared head to head:

• If your program is written in RPE, stick with RPE. Lots of strength programs say things like "3 × 5 at RPE 8". Converting every session is one more step to get wrong.
• If you're new or training for muscle growth, RIR is usually easier. Counting reps left is more concrete than giving a score.
• If you also log warm-ups or cardio, RPE has ratings for easy efforts that RIR doesn't express well.
• Don't mix both in the same log. Pick one and record it the same way every time so you can compare weeks.

RPE load charts: what they are and how far to trust them

You'll find charts online with reps across the top, RPE down the side and a percentage of 1RM in each cell: "5 reps at RPE 8 ≈ this much of your max". The idea is to pick the day's weight from the RPE you're aiming for.

Helms et al. (2016) published one of these, open access, covering RPE 7 to 10 in half points and 1 to 8 reps. We're not reproducing it here; you can see it in the original paper. What matters more is what its own authors say about it:

• Only three cells are measured data. They come from the experienced lifters in Zourdos' back squat study: a single at RPE 10 at 100% of 1RM, a single at RPE 8 at about 91%, and 8 reps at RPE 7 at 70%. Everything else is an estimate.
• It's built on the barbell back squat. The relationship may differ on machines, single-joint lifts or upper-body exercises.
• These are averages, and people vary a lot. For 8 reps at 70%, roughly two-thirds of lifters would report 2 to 4 reps in reserve, but some would say 1 and others 5.
• The authors say to use it to understand how load, reps and effort relate, not as an exact conversion tool.

One more useful data point: in a study of 15 powerlifters, the average RPE given at a true 1RM was 9.6–9.7, not 10, even though the link between percentage of 1RM and RPE was very strong on the squat, bench press and deadlift (Helms et al., 2017). Even experienced lifters rate a max a little short.

RPE or percentages?

One trial compared the two approaches with sets and reps matched. For 8 weeks, 21 trained men squatted and bench pressed three times a week: one group used percentages of 1RM, the other picked loads to hit a target RPE (Helms et al., 2018).

Both groups gained strength and muscle thickness, and the differences between them weren't significant. The RPE group showed a likely small advantage in 1RM. The authors' conclusion: both methods work, and RPE-based loading may give most people a small strength edge. It's a small study in trained men, so don't stretch it further than that.

Whichever scale you use, you'll misjudge at first: on average, people underestimate by almost one rep (Halperin et al., 2021). How to sharpen that estimate is covered in the RIR article, and what happens when you take every set to the limit, in training to failure.

RPE and RIR in MUTARA

MUTARA uses RIR only: every exercise in your routine has a target RIR (for example, "RIR 1–2") and every set is logged with its RIR as a whole number. There's no RPE field.

If your program is written in RPE, subtract it from 10 before you log it: RPE 8 goes in as RIR 2. For half points, round whichever way feels more honest; from there the app suggests the weight for your next session using double progression.