A program can tell you the sets and the reps, but not how hard they should feel, because the same eight reps can be easy one week and a grind the next. Two short names cover that gap. RIR, reps in reserve, is how many more reps you could have done when you stopped. RPE, the rating of perceived exertion, is the same thing on a scale of 1 to 10. Here is how the scale works and how hard a set should be.

The short answer

RPE 10 means you could not have done another rep; each point below it is one rep in reserve, so RPE 9 is one rep left, 8 is two and 7 is three. End most working sets at RPE 7 to 9, one to three reps short of failure. For muscle, going all the way to failure adds little beyond that and costs more fatigue; for strength, how close you go matters even less. Expect to be off by about a rep at first: people tend to have one more in them than they think.

The scale

The first effort scales, from 6 to 20 and later 1 to 10, were mostly used for endurance exercise. For lifting, a 2016 study tied each number to the reps left in the set. A guide to using it explains the lower end: far from failure, nobody can count reps in reserve reliably, so 5 and 6 share one range and 1 to 4 describe effort in words.

RPE Reps in reserve What it feels like
10 0 Maximum effort: no rep left
9 1 One more rep, and that is it
8 2 Two more reps
7 3 Three more reps
5 to 6 4 to 6 Several left, hard to count exactly
3 to 4 Not counted Light effort
1 to 2 Not counted Little or no effort

So for the working sets that matter, RPE and RIR are one scale read two ways: RPE 8 is 2 RIR.

How close to failure

  • Failure is not needed for muscle. A 2023 meta-analysis of 15 studies found no advantage for training to momentary failure over stopping short. In an 8-week trial, 18 trained people did the leg press and the leg extension to failure with one leg and one or two reps short with the other: the thighs grew the same, and failure left more fatigue.
  • Close still matters for muscle. A 2024 series of meta-regressions found muscle growth improved as sets ended closer to failure, while strength gains were similar across a wide range of reps in reserve.
  • The position stand agrees. The American College of Sports Medicine’s 2026 position stand, an overview of 137 reviews, found that training to failure did not consistently change results, and its main advice is simply to train with high effort.
  • Rating works as a way to load. In an 8-week study of the squat and the bench press, trained men who chose their weights to hit a target RPE gained as much as men lifting set percentages of their maximum, with a small edge for the RPE group that was not statistically significant.
Goal RPE Reps in reserve
Muscle, main lifts 7 to 9 1 to 3
Muscle, last set of an isolation exercise 9 to 10 0 to 1
Strength, heavy sets 7 to 9 1 to 3
Warm-up sets, technique practice 5 or less 5 or more
A deload week 6 to 7 3 or 4

How good are you at judging it?

Imperfect, and better than you might think. A 2022 meta-analysis of 12 studies with 414 people found that they underestimated the reps they had left by about one on average. Their guesses were better near the end of a set, in sets of 12 reps or fewer and in later sets, while training experience made little difference. In the 2016 squat study, the reps slowed as the rating rose, so a slowing rep is a useful clue. The guide to the scale suggests that newcomers track the rating beside their normal numbers for a while before relying on it.

What it means for your week

Our programs prescribe reps, not effort: each of the 397 exercise rows in our 25 programs gives sets and reps, a time or a distance, and none gives an RPE or asks for a set to failure. The effort is yours to set, and RPE is how. On the push day of Intermediate Push Pull Legs, 3 days, the Barbell Bench Press asks for 4 sets of 6 to 10: pick a weight that gives you the bottom of the range at about RPE 7 on the first set, and let the last set drift toward 9. When every set reaches the top of the range, add the smallest step, as Progressive Overload describes. The ranges themselves are in How Many Reps Should You Do?

How to apply it

  1. Rate every working set before you rest: how many more good reps were there?
  2. Adjust the weight by the answer. Four or more left: go heavier. None, or form slipping: go lighter. How Much Weight Should You Lift? has the steps.
  3. Keep the big lifts at 7 to 9, and save RPE 10 for the last set of a machine or isolation exercise, where a missed rep simply ends the set.
  4. Calibrate now and then. Take one such last set to failure and compare the reps with your guess.

Trenno asks about effort in two places. When you finish a workout, it asks How hard was this workout? on a scale of 1 to 10 in half steps, and the finished workout shows it as Effort, such as 7.5/10 Hard. Researchers call this the session RPE, and a 2004 study found it reliable for resistance training. Each exercise card also has Easy, Normal and Hard: mark an exercise Easy and the next session suggests a heavier weight. Both ratings, with heavy sets near your best, weigh into the recovery estimate. There is no rating per set: your reps in reserve live in how you choose the next weight.

Mistakes and myths

  • “A set only counts at RPE 10.” Sets one or two reps short built muscle as well in the trial above, with less fatigue.
  • Rating the breathing, not the reps. A set can leave you out of breath and still end far from failure. Ask how many reps were left.
  • Precise numbers far from failure. Four or more reps from failure, the count is rough; that is why the scale groups them.
  • Trusting it blindly. People underestimate by about a rep, experienced lifters included; check a rating against a set taken to failure now and then.

FAQ

Is RPE the same as reps in reserve?

For lifting, on the scale above, yes: RPE 9 is one rep in reserve, 8 is two, 7 is three.

What RPE should a beginner train at?

Around 7 to 8 while learning the lifts: two or three reps short leaves room for the form to hold. Rate every set anyway, and check a rating now and then on a machine.

Should I ever train to failure?

Now and then, on the last set of an isolation or machine exercise, to check your ratings. The studies found no extra growth from failure over stopping one or two reps short.

How do RPE and a rep range fit together?

The range sets the reps, the RPE sets the weight. Choose the weight that gives you the bottom of the range with two or three reps left, then add reps before weight.

Sources