RPE vs. RIR (Reps in Reserve)

In modern strength training and hypertrophy programming, you will often see both RPE (Rate of Perceived Exertion) and RIR (Reps in Reserve) used to prescribe intensity.

While they are mathematically related and often used interchangeably, they stem from slightly different philosophies.

Definitions

• RPE (Rate of Perceived Exertion): A subjective scale measuring overall effort and fatigue, typically from 1 to 10.
• RIR (Reps in Reserve): An objective count of exactly how many more reps you could have completed before reaching muscular failure.

The Mathematical Conversion

For most practical purposes in lifting, RPE and RIR have a direct inverse relationship when the RPE is 7 or above:

RPE = 10 - RIR

Which One Should You Use?

It largely depends on your sport and your goals.

Powerlifting & Strength (Advantage: RPE)

In powerlifting, the goal is 1-rep max strength. An RPE 10 doesn't just mean "I couldn't do another rep." It could mean "I hit my max weight for a single, and it was a grinder."

RPE accounts for the quality of the rep. If you do a heavy single and it moves fast, it's an RPE 8. If you do that same heavy single and it takes 5 seconds to lock out, it's an RPE 10. In both scenarios, the RIR is technically 0 (you aren't doing a second rep), but the effort was vastly different. RPE captures this nuance.

Bodybuilding & Hypertrophy (Advantage: RIR)

In bodybuilding, the goal is to recruit muscle fibers by getting close to failure. The absolute weight on the bar matters less than the proximity to failure.

For a set of 12 bicep curls, asking "Was that an RPE 8 or 9?" can be confusing. It is much more practical to ask "Could I have done 2 more reps?" (2 RIR). Because hypertrophy relies so heavily on taking sets near failure (0-3 RIR), using Reps in Reserve provides a clearer, more direct target.

No matter which system you use, our Calculators can help you find the exact weight you need for your target intensity.