How useful is RPE

It typically ranges from 0 (no exertion) to 10 (maximal exertion).

RPE Scale of 1 to 10, with corresponding intensity, subjective measures, and training zones. Note RPE 1-3 would consist of activities such as sitting on the couch or walking.

Recovery Run = Zone 1

Endurance Run = Zone 2

Steady State Run = Zone 3

Tempo Run = Zone 4

Running Intervals = Zone 5

Not sure this figure entirely corresponds with the above