Some training plans prescribe a fixed weight. Others tell you to work at RPE 8 or finish a set with 2 RIR. Both approaches describe something a percentage alone cannot always capture: how demanding a set is relative to what you could still do.
That matters because strength is not identical from one session to the next. A load that moves comfortably one week can feel considerably heavier after poor sleep, accumulated fatigue or several hard training sessions. RPE training and RIR training allow the load to respond to that difference while keeping the intended effort of the session more consistent.
The two systems are closely related. The main difference is how they describe the same effort.
What does RPE mean in the gym?
RPE stands for Rate of Perceived Exertion.
In strength training, the commonly used RPE scale runs from 1 to 10. The upper end of the scale is linked to how many additional repetitions could still have been completed.
An RPE 10 set leaves no further full repetition in reserve. An RPE 9 set leaves approximately one, while RPE 8 corresponds to roughly two repetitions in reserve.
The idea of rating perceived exertion predates this strength-training system. The original Borg RPE scale runs from 6 to 20 and was developed to describe overall perceived exertion during exercise. It is still encountered in endurance training, running and clinical exercise settings.
When a strength programme prescribes RPE 7, 8 or 9, however, it normally refers to the 1–10 resistance-training scale.
What does RIR mean in the gym?
RIR stands for Reps in Reserve.
Instead of assigning the set an effort score, RIR asks a more direct question:
How many good repetitions could still have been completed?
A set stopped at 3 RIR should leave approximately three repetitions available. At 1 RIR, another repetition should still be possible. At 0 RIR, no additional full repetition is realistically available.
RIR therefore describes proximity to failure directly.
For lifters new to autoregulated training, that can be easier to judge than an RPE value. Rather than deciding whether a set was an RPE 7 or RPE 8, the focus is simply on the number of repetitions left.
RPE vs RIR: comparison table
| RPE value | Approx. RIR | Practical interpretation |
|---|---|---|
| 10 | 0 | No further full repetition available |
| 9 | ~1 | Very hard, with roughly one rep remaining |
| 8 | ~2 | Hard but controlled, with roughly two reps remaining |
| 7 | ~3 | Challenging, with clear room left |
| 6 or lower | ~4+ | Further from failure and increasingly difficult to estimate precisely |
This is a practical relationship rather than an exact conversion formula. The further a set is from failure, the harder it becomes to estimate precisely how many repetitions remain.
That is why RPE and RIR ratings tend to be most useful on genuine working sets rather than very easy warm-up sets.
How RPE training and RIR training adjust the load
Imagine a programme calls for:
3 × 5 at RPE 8
The target is not necessarily one predetermined weight. The aim is to complete five repetitions while finishing with approximately two repetitions still available.
If the first work set is clearly closer to RPE 7, the load can be increased slightly. If those five repetitions unexpectedly become RPE 9 or higher, reducing the next set can bring the session back towards the intended effort.
A prescription of:
3 × 5 at 2 RIR
aims for essentially the same proximity to failure.
Small load adjustments are particularly useful with this type of programming. Having suitable weight plates available makes it possible to increase or reduce the bar in smaller steps instead of forcing a large jump between working sets.
Why an RPE value is not a fixed percentage of 1RM
The RPE scale should not be treated as another rigid percentage chart.
Five repetitions at RPE 8, eight repetitions at RPE 8 and a single repetition at RPE 8 are different prescriptions. The same RPE value can therefore occur at different percentages of 1RM.
Individual repetition capacity also varies. Two lifters with the same one-repetition maximum may perform a different number of repetitions at 80% of that maximum.
This is one of the main reasons to use RPE training in the first place. The load can respond to performance on the day rather than relying entirely on a previously tested maximum.
What does an RPE calculator calculate?
An RPE calculator normally combines the load, number of repetitions and an RPE or RIR rating to estimate values such as an estimated one-repetition maximum.
That can be useful for monitoring trends, but the result depends on the quality of the original rating.
If a set recorded as RPE 8 was actually much closer to RPE 10, the calculated estimate will also be affected.
An RPE calculator is therefore useful for planning and tracking, but it does not objectively measure how difficult a set was.
When does the RPE scale make sense?
The RPE scale works particularly well in programmes that regulate effort across different exercises and repetition ranges.
It also allows finer adjustments. More experienced lifters may use ratings such as RPE 8.5 or RPE 9.5 when a set clearly sits between two whole values.
That flexibility is particularly useful in powerlifting and general strength programming, where the working weight can change while the intended level of effort remains similar.
When is RIR easier to use?
RIR is often straightforward for hypertrophy work, machines and accessory exercises because the target directly describes distance from failure.
- 3 RIR: clear room left
- 2 RIR: hard work with some reserve
- 1 RIR: very close to failure
- 0 RIR: no further full repetition available
There is little need to translate that into another number first.
Neither system needs to replace the other. A programme can use the RPE scale for heavy barbell work and RIR targets for accessory training if that makes the intended effort easier to interpret.
Does productive training require RPE 10?
No. RPE 10 and 0 RIR describe the extreme end of the scale, not the default target for every hard set.
Sets taken closer to failure generally create more immediate fatigue than sets stopped with repetitions in reserve. That does not make training to failure inherently wrong; it means the appropriate target depends on the exercise, the purpose of the session and the current training phase.
Heavy squats, bench presses and deadlifts therefore do not need to be handled exactly like controlled machine or isolation work.
How to get better at estimating RPE and RIR
RPE and RIR ratings are skills rather than perfectly objective measurements.
Early estimates will not always be accurate. They become more useful when exercise, load, repetitions and effort are recorded consistently and compared over time.
On suitable exercises, an occasional set can also be extended beyond the intended stopping point to check whether the estimated RIR was realistic. There is no need to turn every heavy compound lift into a failure test simply to confirm a rating.
Recording those patterns in a training logbook makes it easier to see how a particular load actually behaves across several weeks rather than relying on memory.
With experience, an RPE 8 set or a 2 RIR target becomes a practical reference rather than an abstract number.
RPE or RIR: which should you use?
Both systems can regulate training effectively.
RIR is often easier when the main question is simply how many repetitions should remain before failure. The RPE scale offers more flexibility when effort needs to be compared across exercises, loads and repetition ranges.
The important part is consistency. A rating becomes useful when it helps select and adjust the load from session to session.
FAQ
What does RPE stand for in strength training?
RPE stands for Rate of Perceived Exertion. In strength training, the commonly used 1–10 RPE scale describes how demanding a set was and, particularly at the upper end, can be related to repetitions in reserve.
What does RIR mean in fitness?
RIR means Reps in Reserve. It estimates how many additional full repetitions could still have been completed at the end of a set.
What does an RPE 8 mean in lifting?
An RPE 8 set generally indicates that approximately two further repetitions were available. It is a practical estimate rather than an exact measurement.
How do you calculate an RPE value?
The RPE value itself is a subjective assessment rather than the result of a formula. An RPE calculator can use load, repetitions and the reported RPE value to estimate figures such as an estimated 1RM.