RIR stands for reps in reserve. It is the number of reps a lifter could still have completed when they racked the weight. A client who finishes a set of eight knowing two more were there has done that set at 2 RIR.
Prescribing RIR sets the effort rather than the load. "Squat 5 at 2 RIR" tells the client to pick a weight that leaves two reps in the tank that day, so the same line on the program produces the same effort in week one and in week four.
RIR and RPE measure the same thing
RPE — rate of perceived exertion — counts up to failure. RIR counts down from it. On the ten-point scale used in strength training the two are arithmetic opposites.
| RIR | RPE | The set |
|---|---|---|
| 0 | 10 | Failure. No further rep was possible. |
| 1 | 9 | One rep left |
| 2 | 8 | Two reps left. The standard working set. |
| 3 | 7 | Three reps left |
| 4 | 6 | Four reps left. Light for most working sets. |
| 5 or more | 5 or below | Warm-up territory |
The real difference is what you ask the client. "How many more could you have done?" is a question about a fact. "Rate that out of ten" asks for a judgement against a scale they have to hold in their head. Clients answer the first one more accurately, particularly in their first few months. Which one to write on the program is covered in RPE vs RIR.
Why prescribe reps in reserve
Percentage-based loading assumes a one-rep max that was accurate on the day it was tested, and a client who turns up in the same state every session. Take a 140kg squat and prescribe 8 reps at 70%. That is 98kg on the bar whether the client slept nine hours or four, and whether the max was tested three weeks ago or five months ago.
Written as 8 at 2 RIR, the same session is 90kg in a bad week and 105kg in a good one. Both are the correct session, because the target was the effort. You also find out something from the number the client picked: three weeks of 8 at 2 RIR with the load stuck at 90kg is a recovery conversation, not a programming one.
RIR is also the cleanest way to run intensity across a mesocycle. Start the block at 3 RIR, take a rep off each week, finish at 0–1 RIR before the deload. Volume and exercise selection stay put and the effort climbs on a schedule you can write down.
That only works if the ratings survive the week. Fitsly lets you turn RIR on as a per-set tracking column when you build an exercise, alongside weight and reps, so the rating comes back attached to the set in the training log rather than sitting in a chat message you have to scroll for.
Getting accurate ratings out of clients
Almost every client under-rates their reserve at first — a hard set feels much closer to failure than it is. Four things fix it:
Take one set to genuine failure early, on something safe like a leg press or a machine row. Until a client has hit a real 0 RIR, every other number is a guess against a reference they have never felt.
Ask for reps, not a rating. Put the question in the workout as "how many more could you have done?" and let the number be the answer.
Prescribe a range at first. 2–3 RIR rather than 2 RIR, so a client who is half a rep out is still training where you wanted them.
Cross-check against the load. Consistent 2 RIR reports with no weight moving for a month usually means the client is rating how unpleasant the exercise felt.
Give it four to six weeks. Accuracy improves quickly once there is a real failure set to calibrate against.
Where RIR does not apply
RIR is close to useless for a true beginner. They have no reference for failure and their technique changes enough between sessions that the ratings are not comparable. Use fixed loads and add weight on a schedule until form settles.
It also breaks down on very high-rep and long sets, where the last few reps feel far worse than the reserve suggests, and on speed and power work, where a low effort rating is the whole point.
Conditioning formats are a different job entirely. In an AMRAP the target is rounds inside a fixed window, and in an EMOM the clock sets the work and the rest. Neither is asking the client to stop a set short of failure, so there is nothing for an RIR target to control.
