Your estimated max from a set you did, and the load for any other reps and effort.
Two published steps and nothing else. There is no chart behind this page.
One. RPE is converted to reps in reserve. RPE 8 means two reps left in the tank, so a set of five at RPE 8 was a load you could have taken for seven. That reading of the scale is the one described by Zourdos and colleagues, who built the repetitions-in-reserve version of RPE for resistance training.
Two. That rep count goes into the Epley equation,
1RM = w × (1 + r / 30), and the same equation run backwards gives the load
for any other target. Epley is undefined in the useful sense at one rep, where it claims a
single is three percent heavier than itself, so anything that works out at one rep or fewer is
treated as the max, which is what it is.
What it cannot do. An estimate off ten reps is not the same animal as an estimate off three: the further the set is from a single, the more the formula is guessing. RPE is also a skill rather than a reading. Zourdos found experienced squatters reported it more accurately than novices, which is the honest caveat on every number this page prints: it is only as good as the RPE you gave it.
Why the app gives a different number. This page uses Epley, which works from reps alone and ignores the RPE you typed when it estimates the max. The athlete app reads a published RPE chart instead, the same kind of table as the training maxes guide, and only falls back to a reps-based formula when a set is logged with no rating at all. At three reps those land at about 91, 92 and 94 per cent of a max. None is wrong and all three are estimates of a weight you have not lifted, but they are a few kilos apart on a heavy triple, so do not mix them.
Nothing here is stored and nothing is sent anywhere. The maths runs in your browser.
1 + r/30 equation used above.