General training information only, not medical or coaching advice.
About this tool
The RPE / RIR Calculator links how hard a set felt to a percentage of your one-rep max, using a standard reps-by-RPE chart. It works two ways and runs entirely in your browser with nothing uploaded.
RPE (rate of perceived exertion) runs 6–10, and reps in reserve is simply RIR = 10 − RPE, so an RPE 8 set leaves about 2 reps in the tank. Each reps-and-RPE pair maps to a percentage of 1RM — for instance 1 rep at RPE 10 is 100%, 1 rep at RPE 9 is about 96%, and 5 reps at RPE 8 is roughly 81%. In estimate mode your one-rep max is weight ÷ (percentage ÷ 100). In prescribe mode it multiplies your one-rep max by the chart percentage for your target reps and RPE, then rounds to the loading increment you set.
Use estimate mode after a hard set to gauge your current 1RM, or prescribe mode to pick a working weight for a planned reps-and-RPE target. This is general training information, not medical or coaching advice.
Frequently asked questions
What is the difference between RPE and RIR?
RPE rates effort from 6 to 10, while RIR counts reps left in reserve. They are two sides of the same coin: RIR = 10 − RPE, so RPE 8 means about 2 reps in reserve.
How is the one-rep max estimated?
The chart gives the percentage of 1RM your set represents for its reps and RPE. Your estimated 1RM is the weight lifted divided by that percentage (as a decimal) — e.g. 100 kg at 81% ≈ 123 kg.
How does prescribe mode work?
Enter your estimated 1RM plus a target reps and RPE. It multiplies the 1RM by the chart percentage for that pairing and rounds to your chosen increment to give a practical working load.
How accurate is the RPE chart?
RPE charts are a widely used approximation; real percentages vary by lifter, lift and fatigue. Rate effort honestly and adjust from experience — treat the numbers as a guide, not a guarantee.