RPE, or rating of perceived exertion, isn’t calculated with a formula. It’s a self-reported number you assign based on how hard your body feels like it’s working. There are two main scales used in different contexts: a 6-to-20 scale designed for cardio exercise and a 0-to-10 scale common in both general fitness and strength training. The trick is learning which physical cues to pay attention to so your number is consistent and useful.
The Two RPE Scales
The original scale, created by Swedish researcher Gunnar Borg, runs from 6 to 20. Those numbers look odd, but they were designed to roughly correspond to heart rate when you multiply by 10. A rating of 6 means complete rest (around 60 beats per minute), while 20 represents maximum effort (around 200 bpm). Research on young adults confirmed a reliable relationship between this scale and actual heart rate during dynamic exercise, described by the equation: heart rate equals about 8.88 times your RPE score plus 38.2 beats per minute.
The modified scale, called the Borg CR10, simplifies things to a 0-through-10 range. Zero means no exertion at all, 5 represents hard effort, and 10 is the absolute maximum you can produce. Half-point ratings like 0.5 (“very, very slight effort”) are allowed. This version is more intuitive for most people and has become the default in gym settings.
How to Rate Yourself During Cardio
For aerobic exercise like running, cycling, or swimming, you determine your RPE by checking in with a few physical signals at once: how fast you’re breathing, how fatigued your muscles feel, how much you’re sweating, and whether your heart feels like it’s racing. The most reliable single cue is your breathing rate. Here’s a practical framework using the 0-to-10 scale:
- RPE 2-3 (light): You can hold a full conversation without pausing for breath. This is a warm-up or easy recovery pace.
- RPE 4-6 (moderate): You can speak in sentences but need to breathe between them. This is the zone most people should target for general fitness. It corresponds roughly to 64-76% of your maximum heart rate.
- RPE 7-8 (hard): You can get out a few words at a time but can’t sustain a conversation. Breathing is heavy and deliberate.
- RPE 9-10 (near-max to max): Speaking is impossible. You could only sustain this intensity for seconds to a couple of minutes.
If you want to cross-check your subjective rating against something objective, the original 6-20 scale gives you a rough heart rate estimate. An RPE of 13 (“somewhat hard”) maps to a moderate intensity of about 130-150 bpm for most adults, which aligns well with ACSM guidelines for moderate exercise.
How RPE Works for Strength Training
In the weight room, RPE is calculated differently. Instead of breathing and heart rate, you base your score on how many reps you had left in the tank when you stopped. This concept is called Reps in Reserve, or RIR, and it flips the scale so that higher numbers mean harder sets.
The RIR-based RPE scale works like this:
- RPE 10: Maximum effort, 0 reps in reserve. You could not have done another rep.
- RPE 9: 1 rep left in reserve.
- RPE 8: 2 reps left in reserve.
- RPE 7: 3 reps left in reserve.
- RPE 5-6: 4-6 reps left in reserve.
So if your program says “3 sets of 5 at RPE 8,” you should pick a weight heavy enough that you finish each set of 5 feeling like you could have done 2 more reps, but not 3. If you finish and realize you had 4 reps left, the weight was too light. If you barely grind out the fifth rep, it was too heavy for that prescription.
Why RIR Matters for Programming
This system solves a real problem: your strength fluctuates day to day based on sleep, stress, nutrition, and accumulated fatigue. A weight that feels like RPE 7 on Monday might feel like RPE 9 on Thursday. Rather than locking you into a fixed number on the bar, RIR-based RPE lets you auto-regulate. Research on this approach suggests that for main compound lifts like squats and bench press, most training sets should fall in the RPE 6-8 range (2-4 reps in reserve) to build strength without excessive muscle damage. Sets targeting muscular endurance can push to RPE 9-10 with higher rep counts of 12 or more.
As a practical example, say your coach prescribes “3 sets of 10 at RPE 8-9.” That means you should finish each set of 10 with only 1 or 2 reps to spare. If you’re doing power-focused training with heavy loads above 80% of your max, you’d typically stay at RPE 7-8, stopping each set with 2-3 reps still available.
Your Estimates Get More Accurate Over Time
Research shows that people are significantly better at estimating their remaining reps when they’re closer to failure. If you have 1 or 2 reps left, you’ll probably nail that assessment. If you have 5 or 6 left, your estimate is fuzzier, which is why the RIR scale groups those values together rather than assigning each one a precise number.
Beginners tend to overestimate how close they are to failure. You might rate a set as RPE 9 when you actually had 3-4 reps left. This is normal and improves with practice. One way to calibrate is to occasionally take a set to true failure on a safe exercise (like a machine press or leg press) and note what that final grinding rep actually feels like. Once you have that reference point for RPE 10, it becomes easier to gauge everything below it.
For cardio, pairing your subjective rating with a heart rate monitor for a few weeks gives you a personal baseline. Interestingly, a 14-week study comparing people who used RPE alone versus heart rate monitors to guide their workout intensity found that the RPE group improved their endurance by 11%, while the heart rate group improved by only 6%. The subjective approach may work better because it accounts for variables that heart rate alone misses, like heat, dehydration, and cumulative fatigue.
Putting It Into Practice
Rate yourself at the end of each set or each interval, not in the middle. During a set of squats, your brain is busy stabilizing the load. Wait until you rack the bar, then ask: how many more could I have done? For cardio, check in every few minutes or at the end of a sustained effort block.
Keep a training log with your RPE ratings next to weights and distances. Over a few weeks, patterns emerge. You’ll notice that your squat at 185 pounds for 5 reps is consistently RPE 7 when you’re well-rested and RPE 8.5 after a bad night of sleep. That data becomes the foundation of smarter training: on good days you push the weight up, on bad days you pull it back, and your long-term progress stays on track either way.