How Hard Should It Feel? A Beginner's Guide to RPE and RIR

Your program says 3 sets of 10. You do 10 reps, put the dumbbells down, and wonder whether that was enough. Could you have done 11? 15? Was it supposed to feel harder than that?

"Pick a weight that feels hard" is good advice until you try to follow it. Hard compared to what?

Two simple tools answer that question: RIR and RPE. The names sound technical, but both come down to one thing you can check at the end of any set: how many more could I have done?

RIR: how many more could you have done?

RIR stands for reps in reserve. It's the number of reps you had left when you put the weight down.

Say you do 10 goblet squats and stop. If you could have done 2 more before your form changed, that set was 2 RIR. If you could have done 6 more, it was 6 RIR, and the weight was too light.

One detail matters here: only good reps count. A good rep looks like your first rep, with the same range of motion and a controlled lowering. A rep you'd have to twist, bounce or rush to finish is not in your reserve. (More on what makes a real rep in the starting weights guide.)

RPE: the same question, flipped

RPE stands for rating of perceived exertion. You rate the set from 1 to 10, where 10 means you had nothing left.

For lifting, the two scales are mirror images. Two reps in reserve is RPE 8. Three in reserve is RPE 7. This lifting version of the scale was introduced by Zourdos and colleagues in 2016, and it is the one most strength coaches use today.

If you've seen RPE on a treadmill or in a cardio class, that's a different scale that rates how out of breath you are. In the weight room, RPE is about how close a set took you to your limit.

Which one should you use? Start with RIR. Counting the reps you had left is more concrete than rating a feeling, and you can always convert.

Where to aim: 2 to 3 reps left

For most of your working sets, stop with 2 or 3 good reps left. That's RPE 7–8.

At that level, the last couple of reps slow down and take real focus, but your form holds. It's hard enough to make you stronger and controlled enough to keep you safe while you're still learning the movements.

Two adjustments:

• Learning a new exercise? Leave 4 in reserve for the first week or two. Get the movement right, then make it harder.
• Feeling great? Leaving 1 in reserve on your last set now and then is fine.

You don't need to go to failure

Training to failure means lifting until you can't complete another rep. It has a reputation as the only "real" way to train, and the research doesn't support that. A 2023 meta-analysis found no evidence that going to failure builds more muscle than stopping short of it (Refalo et al., 2023).

Failure also costs more: form breaks down, you need longer to recover, and it's the point where beginners are most likely to get hurt. Stopping with 2 or 3 reps left gives you the benefit without the cost.

The more common mistake is going too easy

When researchers let people choose their own weights, most pick loads that are too light. One review put the average at about half of what people could lift once (Steele et al., 2022). In a study of women in their 60s who were new to lifting, the self-selected weights ranged from about a third to a half of their max, below what guidelines recommend for building strength (Elsangedy et al., 2013).

If you finish a set and could have done 6 more, that was a warm-up. RIR gives you a way to notice.

Why the rep range matters too

RIR tells you how hard a set was. It doesn't tell you how heavy the weight was, and for your bones, heavy matters.

You could reach 2 reps in reserve with a light weight by doing 25 reps. Your muscles would still get a training effect. Your bones respond to something else: how much load they have to bear.

• In a year-long trial, postmenopausal women trained with either a weight they could lift 8 times or a lighter weight they could lift 20 times. Both groups got stronger. Only the heavier group gained bone density, at several hip and forearm sites (Kerr et al., 1996).
• A meta-analysis in postmenopausal women found that higher-intensity exercise did more for bone density in the lower spine than low or moderate intensity (Kistler-Fischbacher et al., 2021).
• The UK consensus statement on exercise for osteoporosis advises building up gradually to heavy loads, defined as the most you can lift 8 to 12 times (Brooke-Wavell et al., 2022).

Bone loss speeds up around menopause, which is why this matters so much in midlife. So the full instruction has two parts: choose a weight you can lift 8 to 12 times, and stop with 2 or 3 reps left. If you could sail past 12, the weight is too light. Go up.

If you have osteoporosis, a spinal fracture, or a history of fractures from minor falls, lifting is still recommended for most people, but ask your doctor or a physiotherapist how to start.

How to tell how many you have left

This is the part that takes practice. Three signals help.

1. Watch your rep speed. As you get close to your limit, reps slow down even though you're pushing just as hard. If your last rep was clearly slower than your first, you're around 2 in reserve. If every rep moved at the same speed, you have 4 or more.
2. Let form set the limit. The moment you'd need to change something to finish a rep (shorten the range, arch your back, drop the weight fast on the way down), you're at zero.
3. Ask the honest question. Right after the set: "If I had to, how many more could I have done?" Answer quickly. Your first answer is usually the best one.

Burning muscles and heavy breathing are less reliable signals. A set can feel uncomfortable long before you're near your limit, especially with lighter weights and higher reps.

Calibrate once in a while

Your guesses get better when you check them. Every few weeks, run a calibration set:

1. Pick a simple, stable exercise: a machine chest press, leg press, seated row, lat pulldown or dumbbell curl.
2. On your last set, pause at your usual stopping point and guess how many reps you have left.
3. Keep going until your form is about to change. Count the extra reps.
4. Compare the two numbers.

Don't do this with barbell lifts, or with any exercise where you could get stuck under the weight or lose your balance.

Most people are surprised. Across 12 studies, lifters stopped about one rep earlier than they thought, on average (Halperin et al., 2022). In a 2025 study of adults in their late 60s, people aiming for 2 reps in reserve stopped about 2 reps sooner than that (Gómez-Redondo et al., 2025).

That's the pattern to expect: you have more in you than you think. The same research shows guesses get more accurate close to the limit and in sets of 12 reps or fewer, which is one more reason to train in the 8–12 range.

Common mistakes

• Stopping when it burns. Discomfort shows up early. It isn't the same as being near your limit.
• Counting sloppy reps. If the reps you had "left" would have looked different from your first, they don't count.
• Chasing a 10. Harder isn't always better. RPE 7–8 is the target.
• Expecting precision. Being off by a rep is normal, even for experienced lifters. A rough number you write down every session beats a perfect one you never record.

Using it week to week

Write down three things for every working set: weight, reps and RIR. Then let those numbers decide what happens next time.

1. Pick a rep range, such as 8–12, and aim for 2–3 in reserve.
2. Each session, try for one more rep with the same weight.
3. When you reach the top of the range on every set with 2 or more still in reserve, add weight next time: about 2–5 lb for upper body and 5–10 lb for lower body.
4. If you're down to 1 or 0 in reserve before you reach the bottom of the range, take a little weight off.

Two things worth knowing:

• Easier is progress. If 20 lb for 10 reps was 2 in reserve in week 1 and 3 in reserve by week 3, you got stronger, even though the numbers on the dumbbell didn't change.
• Rough days still count. When sleep, stress or symptoms make everything feel heavier, keep the effort the same and let the weight drop. A set at 2–3 in reserve with a lighter dumbbell is still a good set.

Need somewhere to write it all down? My free workout log has a column for RIR on every set.

The takeaway

At the end of your next set, ask one question: how many more good reps could I have done? Write the number down. If it's more than 3, pick up the heavier weight.

New to lifting? Start with the free 5-Day Perimenopause Strength Starter.

Ready for a full plan? The 4-week Beginner Strength program uses these targets in every session.

Want the bigger picture? Read the beginner's guide to strength training in perimenopause.

This article is general education, not medical advice.