Rating of Perceived Exertion Scale (RPE) was created by Borg (1970). It is a subjective measure of exercise intensity. You should know that the scale ranges from 6-20 and can be seen below.

You need to be able to calculate heart rate from RPE, and RPE from heart rate. The relationship between RPE and heart rate is: RPE x 10 = HR (bpm) or HR divided by 10 = RPE

For example, if i am working at level 9 on RPE, i am considered to be working at 90 bpm. If i am working at 14 RPE then i am considered to be working at 140bpm.

If i am working at 120 bpm then i am working at 12 on RPE.

On RPE you do not round up, you always round down. For example, 145bpm would always be 14 on RPE, 162 will be 16 on RPE.