Reps in reserve
RIR = 10 − RPE. An RPE 8 set leaves ~2 reps in reserve.
Convert a target RPE and rep count into a working weight from your estimated 1RM. Based on reps-in-reserve and %1RM.
Turn a target RPE and rep count into an actual working weight from your estimated 1RM — the same autoregulation logic adaptive programs use to set daily loads.
Quick answer. To find a working weight from RPE, convert RPE to reps-in-reserve (RIR = 10 − RPE), add it to your target reps, and read that as a percentage of your 1RM. For example, 5 reps at RPE 8 (2 RIR) is about 80% of your 1RM.
RPE (Rate of Perceived Exertion) and its cousin RIR (Reps In Reserve) let you autoregulate load to how you feel that day. An RPE of 8 means you left about 2 reps in the tank. This calculator converts your target reps and RPE into a percentage of your 1RM, then into a concrete weight — so 'work up to a 5 at RPE 8' becomes a number you can load.
RIR = 10 − RPE. An RPE 8 set leaves ~2 reps in reserve.
%1RM = 1 ÷ (1 + (reps + RIR) ÷ 30). Working weight = e1RM × %1RM. Treating reps + RIR as 'reps to failure' keeps the estimate consistent with the 1RM formulas.
RPE is Rate of Perceived Exertion on a 1–10 scale. In strength training it usually maps to reps in reserve: RPE 10 is true failure, RPE 8 leaves about 2 reps in the tank.
Combine target reps with reps-in-reserve (10 − RPE) to get reps-to-failure, then apply a %1RM formula. This calculator does it automatically.
Neither is strictly better. Percentages are simpler to plan; RPE adapts to daily readiness. Many programs use percentages as a target and RPE as a daily governor.
For hypertrophy and general strength, RPE 7–9 covers most working sets. Save RPE 9.5–10 for tested singles or peaking, and keep technique work at RPE 6–7.