Evidence guide
RPE and RIR describe effort, not a fixed weight
Repetitions in reserve (RIR) is your estimate of how many technically acceptable reps remained when the set stopped. The resistance-training RPE scale links that estimate to a 6–10 score: RPE 10 corresponds to 0 RIR, RPE 9 to about 1 RIR, RPE 8 to about 2 RIR, and so on.
The original validation study found an inverse relationship between bar velocity and RPE/RIR in both experienced and novice squatters. Later work found that lifters generally judge RIR more accurately when a set is closer to failure and uses lower-to-moderate repetitions. It is a learnable estimate, not a direct measurement.
How the load estimate is calculated
effective reps = target reps + estimated RIR
load = e1RM ÷ (1 + effective reps ÷ 30)
The calculator combines the RPE/RIR mapping with an inverse Epley equation. For example, 5 reps at RPE 8 is treated as roughly 7 reps of current capacity: five completed plus two in reserve. The result is rounded to your selected plate increment.
This is a transparent planning heuristic, not a validated universal RPE loading chart. Exercises, equipment, repetition speed, fatigue, and individual endurance all change the load–rep relationship. Start with the estimate, then adjust to the effort you actually experience.
A practical calibration habit
- 1
Before the set, choose a target repetition count and RPE.
- 2
Stop at the target and record your estimated RIR before looking at the next load.
- 3
Occasionally—when appropriate for your program—compare the estimate with the reps you could actually complete. Use that feedback to calibrate future ratings.
