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What RIR means and how to log it

RIR is reps in reserve: the number of clean reps you had left when you racked the weight. It is the simplest honest measure of how hard a set was, and it is why two lifters logging "135 for 10" can be doing very different training.

Updated 29 September 2026 · Describes the current App Store release of Mesolab.

The definition

After a set, ask: if I had kept going with the same form, how many more reps would I have completed? That number is your RIR.

• 0 RIR: you could not have done another rep. This is failure.
• 1 RIR: one more was there, and it would have been a grind.
• 2 RIR: two more, the last one slow.
• 3 RIR: three more; the set felt hard but controlled.
• 4+ RIR: comfortably short of the limit. Useful for warm-ups and technique work, not for most working sets.

RIR is the same idea as RPE turned the other way round: RPE 8 is 2 RIR, RPE 9 is 1 RIR, RPE 10 is 0 RIR. Mesolab uses RIR because counting reps you have left is easier to picture mid-set than rating effort on a ten-point scale.

Why it matters for building muscle

Muscle growth responds to sets taken close to failure. The practical range most hypertrophy programs use is 1 to 3 RIR for working sets: close enough to failure that the last reps are genuinely hard, far enough from it that you can repeat the work across a week and a training block without technique breaking down or recovery falling behind.

Weight and reps alone cannot tell you where a set landed. 135 lb for 10 at 4 RIR is a warm-up; the same 135 for 10 at 1 RIR is a limit set. Logging RIR is what turns a rep count into a record of effort, and it is what lets the next session build on this one rather than guess.

How to estimate it honestly

1. Judge bar speed on the last rep. If the last rep moved as fast as the third, you had several left. If it slowed noticeably, you were within two or three. If it nearly stalled, that was 0 or 1.
2. Calibrate occasionally. Once in a while, on a safe exercise (a machine or a dumbbell movement), take a set to actual failure and see how many reps came after the point you would normally have stopped. Most people discover they had more in reserve than they thought.
3. Count reps you could do with the same form. Reps you could grind out with a hitch in your back do not count.
4. Log what happened, not what was planned. If the target was 2 RIR and you hit failure, write 0. The record is only useful if it is true.

Beginners: RIR estimates are rough for the first few months, and that is fine. Consistency matters more than precision. Keep logging it; the estimate sharpens with every set you compare against the last.

What Mesolab does with the RIR you log

Every programmed set in Mesolab shows a rep range and a target RIR next to the weight. When you finish the set you enter the weight, the reps and the RIR you actually reached. From there:

• The target RIR is part of how a suggested weight is calculated, so the app aims you at a load that should land near the intended effort rather than at a number lifted off a percentage chart. See how suggested weights use your history.
• Your logged RIR sits beside the weight and reps in your history, so when you look back at a session you can see whether 140 for 10 was easy or a limit.
• Within a training block the target RIR holds steady through the normal weeks and eases for the deload. Progression comes through sets and load; a hard set means the same thing in week four as in week one.

In Freestyle workouts there is no prescription; you enter the weight, reps and RIR you completed, and the log is yours to read.

Common questions

Should I train to failure?

Occasionally, on isolation and machine work, it is a useful calibration and a hard stimulus. On heavy compound lifts the cost in fatigue and technique usually outweighs the benefit. A program that keeps most working sets at 1 to 3 RIR gets most of the growth for far less wear.

Is 0 RIR better than 2 RIR?

Per set, slightly. Per week, rarely, because sets at 0 RIR cost more recovery, and total quality work over the block is what adds up.

What if I cannot tell?

Pick the number you are least confident about and err toward fewer reps in reserve. Then calibrate on a safe exercise next session.