RPE / RIR Calculator (estimated 1RM & load)

Understanding the RPE and RIR calculator — concept and principle

RPE (rating of perceived exertion) in strength training is a 1–10 score of how hard a set felt, defined by how many more reps you could have done: RPE 10 means no reps left, RPE 9 one rep in reserve (RIR), RPE 8 two. This calculator uses the RTS RPE chart popularised by Mike Tuchscherer to estimate your one-rep max (1RM) from any set of 1–10 reps and to pick the load for a planned set, such as "3 reps at RPE 9".

Reps done plus reps left show how close the set was to failure.

How it is calculated

Look up the chart percentage for the set you did: %1RM = chart(reps, RPE).
Estimated 1RM = weight lifted ÷ %1RM × 100.
Load for the target set = estimated 1RM × chart(target reps, target RPE) ÷ 100.

The chart starts at 100% for 1 rep at RPE 10 and falls with each step. Every 0.5 RPE below 10 counts like half an extra rep, so a set's position in the chart is (reps − 1) + (10 − RPE) whole-rep steps.

The principle

If you stop with two reps in reserve, that weight is roughly the weight you could lift for reps + 2 to failure. A 5-rep set at RPE 8 therefore sits where a 7-rep max would, and the chart gives the percentage of 1RM typical for that rep max. Converting both the completed set and the target set to "reps to failure" puts them on one scale, so a single estimated 1RM links them.

Worked example

Inputs: 100 kg for 5 reps at RPE 8; target 3 reps at RPE 9.
5 reps at RPE 8 equals about 7 reps to failure; chart value 81.1%.
Estimated 1RM = 100 ÷ 81.1 × 100 ≈ 123.3.
3 reps at RPE 9 equals about 4 reps to failure; chart value 89.2%.
Target load = 123.30 × 0.892 ≈ 109.99; the rounded row shows 110 · 110 (nearest 2.5 kg or 5 lb).

Each point is the calculator re-run with only “Weight lifted (kg or lb)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Weight lifted (kg or lb)	Estimated 1RM
25	30.83
50	61.65
75	92.48
100	123.3
125	154.13
150	184.96
200	246.61

How to read the result

The estimated 1RM is a working estimate for programming, not a tested max; it is most accurate from low-rep sets at RPE 8–10. The rounded row snaps the load to 2.5 kg or 5 lb steps; adjust further to the plates you have. If the target set feels clearly easier or harder than planned, adjust the next set by roughly 2–4% per RPE point.

Common mistakes

Misjudging reps in reserve; beginners often think fewer reps are left than really are, which makes the 1RM estimate too low.
Using sets of more than 10 reps, where the chart is not valid.

Keep in mind: The chart is an average across lifters. Your own percentages may differ by several percent, especially on lifts with long ranges of motion. Do not attempt a true max based only on an estimate, and use a spotter for heavy sets.

Frequently asked questions

What is the difference between RPE and RIR?

They describe the same thing on reversed scales: RIR counts reps left, and RPE = 10 − RIR for sets at RPE 7 and above.

Is RPE training good for beginners?

It works, but new lifters rate reps in reserve less accurately. Using it alongside fixed percentages for a few months helps calibrate.

Why does the calculator stop at 10 reps?

The RTS chart covers 1–10 reps, and rep-based 1RM estimates lose accuracy with higher reps.

Sources: Reactive Training Systems RPE chart (M. Tuchscherer) · Zourdos M. C. et al., Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve, Journal of Strength and Conditioning Research, 2016

Checked 8 Nov 2026. Reactive Training Systems RPE chart (M. Tuchscherer).

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