"Do 3 sets of 5 at RPE 8." It's one of the most useful instructions a coach can give, and one of the most confusing for a client who has never used it. Here is what RPE and RIR mean, how they connect to percentages of a one rep max, and how to turn them into a weight on the bar.
RPE and RIR in one minute
RPE (rating of perceived exertion) on a 1 to 10 scale says how hard a set was. In strength training it is read as reps in reserve (RIR): how many more good reps the lifter could have done.
- RPE 10: no reps left
- RPE 9: one rep left
- RPE 8: two reps left
- RPE 7: three reps left
- Half points, like RPE 8.5: maybe two, definitely one
From RPE to a percent of 1RM
Add the reps done and the reps in reserve. That's the number of reps the lifter could have done to failure. A set of 5 at RPE 8 means about 7 reps were possible, so it was roughly a 7-rep max.
A standard RPE chart turns that into a percent of one rep max. A 7-rep max is about 81% of 1RM, a 3-rep max about 92%, a single about 100%.
A worked example
Your client squats 100 kg for 5 at RPE 8.
- 5 reps + 2 in reserve = about a 7-rep max ≈ 81.1% of 1RM
- Estimated 1RM = 100 ÷ 0.811 ≈ 123.3 kg
- Next session: 3 reps at RPE 8.5, which is about 87.8% of 1RM
- 123.3 × 0.8775 ≈ 108.2 kg, rounded down to 107.5 kg with 2.5 kg steps
No max test needed, and the load already fits how the client felt last session.
Why coaches use RPE
Percentages assume the lifter is the same every day. They are not. Sleep, stress and diet change what 85% feels like. RPE lets the load move with the lifter: on a good day the same RPE 8 is a little heavier, on a bad day a little lighter, and the training effect stays similar.
Where RPE goes wrong
- New lifters misjudge it. Most beginners think they are closer to failure than they are. Pair RPE with a load range for the first few months.
- High-rep sets are hard to rate. Above about 10 reps the estimate gets loose.
- It's a starting point. Use the chart for the first set, then let the RPE of that set adjust the rest.
Do it without the chart
Our free RPE calculator estimates a 1RM from any set, gives the working weight for any reps and RPE rounded to your plates, and shows a full table of loads in kg or lb.
When it's time to plan the next block, our Program Progression skill for Claude reads a client's training log, shows what progressed and what stalled lift by lift, and writes the next 4-week block with loads, reps and RPE targets.
A coaching aid, not medical advice. Pain, dizziness or form breaking down are reasons to stop the set, not to hit a number.