RIR vs RPE: what each means, how they convert, and how Method stores both

Two scales, one quantity

Both scales answer the same question about a set. How close to failure was it?

Reps in reserve (RIR) answers it directly. You stop a set of squats and judge that you had two more in you. That is 2 RIR. Zero means the last rep was the last rep you could do.

Rate of perceived exertion (RPE) answers it as an effort score out of 10. In the resistance-training scale described by Zourdos and colleagues, RPE 10 means no reps left, RPE 9 means one left, RPE 8 means two left, and half points sit between [1]. Helms and colleagues set out how to program with that scale [2].

So for lifting they convert exactly.

RIR = 10 − RPE
RPE = 10 − RIR

RPE 8 is 2 RIR. RPE 9.5 is 0.5 RIR. RPE 6 is 4 RIR.

When each one reads better

RIR is easier to act on mid-set and easier to use in arithmetic. A prescription of "8 reps at 2 RIR" tells you exactly when to stop, and the estimated 1RM formula wants reps plus reps in reserve. Most people find it more honest at low intensities, because "4 in reserve" is a concrete claim while "RPE 6" can drift into "it felt easy".

RPE is familiar to anyone who has trained under a powerlifting program, and it handles the top end more naturally. "RPE 9.5" says "I might have had one more" without committing to a whole rep. Many programs are written in RPE and you will want to read them as written.

Neither is more correct. Whichever scale you use, the judgement is more accurate close to failure than far from it. In a study of 81 adults, the error in estimated repetitions to failure was about one rep when 0 to 5 reps remained and more than two reps when 7 to 10 remained, and training experience did not change the accuracy [3]. A scoping review and meta-analysis of 12 studies found people tended to underpredict the reps they had left by about one, with accuracy slightly better closer to failure and in sets of 12 reps or fewer [4]. A set you rate at 5 RIR is a rough guess. A set you rate at 1 RIR is usually close.

Half values

Both scales are useful in halves. A set between 1 and 2 reps in reserve is common, and RPE 8.5 is standard notation. Method stores intensity as a decimal, so prescriptions and logged sets can carry 1.5 RIR or RPE 8.5, and the suggested-load calculation uses the fractional value.

How Method stores and shows it

Every intensity in Method, in a prescription or on a logged set, is stored as canonical reps in reserve. Your account has a preference, RIR or RPE, and the preference is a display lens. It controls how targets are written in the program editor, how the logging screen asks you to rate a set, how analytics labels intensity, the name and values of the intensity column in CSV export, and the wording of suggested-load explanations. Change the preference and all of those update together. The stored value does not move.

This matters for one practical reason. A program written in RPE, logged in RIR, and exported in RPE is the same program, the same log, and the same numbers. Nothing is lost to a conversion step.

Where the number is used

• Estimated 1RM. Effective reps are logged reps plus reps in reserve, folded into the Epley estimate. See Estimated 1RM.
• Suggested loads. The reps in reserve on your last eligible set and the target for the next set are both inputs. See how Method suggests loads.
• Prescriptions. Every set can carry an intensity target in either scale, with decimals.
• Export. The CSV column is called rir or rpe depending on your preference, and the values are converted to match.

A note on what RIR and RPE do not tell you

They describe proximity to failure for that set on that day. They do not diagnose fatigue, readiness, or whether a program is working. A set at 0 RIR after poor sleep and a set at 0 RIR when fresh are both true records. Method records what you logged and leaves the interpretation with you.