RIR vs. RPE: What's the Difference — and Which Should You Use?

RPE 8 and RIR 2 describe almost the same situation in strength training: you end the set and estimate that roughly two clean reps were still available.

The difference lies mainly in how you express the same information. RIR counts the remaining reps directly. The strength-training-specific RPE scale rates the effort on a scale up to 10.

So what matters in practice is less which abbreviation you prefer. It matters more whether you can judge the scale consistently and know where its limits are.

RPE and RIR in one minute

Near muscular failure the relationship is therefore easy to remember:

RPE 8 ≈ RIR 2
RPE 9 ≈ RIR 1
RPE 10 ≈ RIR 0

The ≈ is deliberate. These scales are practical judgements, not measuring instruments.

For quick reference during training there is the RPE table with the common levels and examples.

What does RPE mean in strength training?

RPE stands for rate of perceived exertion — how hard the effort feels subjectively.

The term is older than the scale now common in strength training. Gunnar Borg originally developed RPE scales for general exertion in endurance work. For strength training, a repetition-based 1-to-10 scale was later established, in which the upper levels are tied directly to remaining reps.

A common framing looks like this:

So when a plan prescribes 3×8 @ RPE 8, the practical instruction is:

Choose a weight such that after eight reps, roughly two technically clean reps would still have been possible.

That is more information than “3×8” alone, because the prescription accounts for how you feel that day.

What does RIR mean?

RIR stands for reps in reserve.

The question is even more direct:

How many reps could I still have completed cleanly at the end of the set?

A set at RIR 2 is therefore not a fixed weight and not a fixed rep count. 80 kg × 5 can be RIR 2 — so can 60 kg × 12.

That is exactly what makes RIR intuitive for many: you do not have to translate a scale, you answer one concrete question.

RPE = 10 − RIR: useful, but not unlimited

The familiar formula

RPE = 10 − RIR

works well as a mnemonic in the range where the strength-training-specific RPE scale is tied to reps in reserve.

For RIR 0 to 3 it fits cleanly:

The further a set is from failure, though, the less useful a mathematically exact translation becomes.

Whether a very easy set was “RIR 7”, “RIR 9” or “RPE 3” can hardly be judged reliably — and for managing training, that precision is usually not needed anyway.

RPE and RIR become practically relevant mainly on demanding working sets.

RPE, RIR and %1RM describe different things

This is where confusion often arises.

%1RM describes the load.
RPE and RIR describe the effort, or the distance from failure.

So there is no fixed statement like:

RPE 8 = 80 % of 1RM.

Suppose you do three reps at RPE 8. By your own judgement, you could have managed about five reps in total.

If instead you do ten reps at RPE 8, your estimated maximum for that set would be around twelve reps.

The loads have to differ accordingly.

The following table shows this only as a worked example. It uses the Epley formula, which the 1RM calculator also uses, and assumes that reps performed plus RIR roughly equal the maximum possible rep count.

The most important point is not any individual figure but the spread: the same RPE value can go with very different percentages depending on the rep count.

And even this table is not an individual truth. Rep performance at a given %1RM differs between people, exercises and training levels. On top of that, 1RM estimation formulas get less accurate at higher rep counts.

As orientation the table works. As an exact load prescription it does not.

Which system is more accurate?

Neither RPE nor RIR is automatically more accurate, because both depend on the same ability: you have to judge how close to failure you actually are.

The research shows a fairly plausible pattern here: RIR estimates tend to be more accurate when

• the set is closer to failure,
• the load is relatively high,
• and the judgement is made later in the set.

On a set that is maybe eight or ten reps away from failure, nobody can feel that reserve particularly precisely. At RIR 1 or 2 the task is considerably more concrete.

Also interesting: training experience does not help as unambiguously in every study as you might intuitively expect. Experienced lifters can use the scales very well, but “beginners are generally off by 1–2 points” would be too sweeping.

The larger source of error is usually not the choice between RPE and RIR, but the distance from failure.

How to calibrate RPE and RIR

You do not have to take sets to absolute muscular failure every week. Without an occasional reality check, though, RIR easily stays a theoretical number.

A practical calibration works like this:

1. Pick an exercise you are technically confident with.
2. End a working set at an estimated RIR 2.
3. Note your estimate.
4. Occasionally — not constantly — continue in a suitable set under control and check whether roughly two reps really were still available.
5. Compare across several weeks whether your estimate is improving.

Machines and safe isolation exercises are often better suited to tests like this than a heavy squat without a spotter.

The point is not to fail as often as possible. The point is to give your subjective scale an occasional reality check.

When RPE makes more sense

RPE is particularly practical when your program already works with it.

RPE fits well when:

• your plan uses prescriptions like “3×5 @ RPE 8”,
• you work with half-steps like 8.5,
• your coach uses the same scale,
• you want to steer load and daily readiness together.

Which is why RPE is widespread in powerlifting and in autoregulated programs.

The advantage of half-steps should not be confused with genuine measurement precision, though. RPE 8.5 looks more precise than a subjective judgement necessarily is.

When RIR makes more sense

RIR is often more direct as language.

RIR fits well when:

• “two more reps” is more intuitive for you than “RPE 8”,
• you are introducing new lifters to proximity to failure,
• you steer hypertrophy training through a target range like RIR 1–3,
• you deliberately do not need half-steps.

With heuristics like effective sets, RIR is also easier to communicate. You just have to keep in mind: a fixed boundary like “RIR 0–3 = effective, RIR 4 = worthless” is not a biological dividing line. The value of a set does not suddenly drop off at a number on the scale.

RPE/RIR and percentage training are not opposites

RPE and RIR are frequently presented as an alternative to percentage prescriptions. In practice, both systems combine well.

A program can prescribe a load range and additionally say:

Work at roughly RPE 8 today.

The percentage then provides the rough structure while RPE accounts for daily readiness.

That is particularly helpful because your actual capacity does not match your long-term 1RM exactly every day. At the same time, percentage training has an advantage: it is objective and easy to plan.

So the interesting question is not “RPE or percentages?” but which tool should do which job?

→ RPE vs. percentages: which system is better?

Logging RPE and RIR in training

In the workout screen you can record RPE or RIR for every set.

The real value does not come from any individual number but from the trend.

If you train 100 kg × 5 across several weeks and the set drops from RPE 9 to RPE 8, that is an indication the same load is moving more easily — even if you set no new PR that day.

Conversely, an unusually high RPE at familiar weights can show that sleep, stress or previous training are playing a role today.

The plans in hitPR can still drive their progression through fixed rules like AMRAP, double progression or scheme changes. RPE and RIR add your subjective load to that data.

Conclusion

RPE and RIR are not rival systems in strength training.

In the relevant range close to failure, they describe essentially the same information from two directions:

• RIR 2 asks: how many reps were left?
• RPE 8 says: how demanding was the set on the repetition-based ten-point scale?

The familiar conversion is useful, but not as exact as the numbers make it look. The further you are from failure, the less certain the judgement.

If your program uses RPE, use RPE. If “two reps in the tank” feels more intuitive, use RIR.

The better scale is the one you can apply consistently and calibrate sensibly over time.

Further reading:

• What are effective sets?
• Training Max explained

Sources

• Zourdos MC et al. (2016). Novel Resistance Training-Specific Rating of Perceived Exertion Scale Measuring Repetitions in Reserve. Journal of Strength and Conditioning Research, 30(1):267–275.
• Helms ER et al. (2018). RPE and Velocity Relationships for the Back Squat, Bench Press, and Deadlift in Powerlifters. Journal of Strength and Conditioning Research, 32(2):292–297.
• Halperin I et al. (2024). Feasibility and Usefulness of Repetitions-In-Reserve Scales for Selecting Exercise Intensity: A Scoping Review. Sports Medicine - Open.
• Russo F et al. (2025). Factors influencing the accuracy of the repetition in reserve scale in resistance training: a systematic review. Physical Therapy Reviews.