The Rating of Perceived Exertion (RPE) is a rating scale ranging from 1-10 that helps you to identify how hard you are working. The original scale, the Borg Scale, worked from 6-20, but was quite confusing. The RPE or modified Borg Scale is much more simple to use.
The perceived exertion is based on how you FEEL during exercise. Whilst you’re running, think about your overall levels of physical stress and fatigue. Don’t think about just one thing such as how your legs feel, or how heavily you are breathing. It’s an overall measure of how hard you are working. Try to concentrate on you overall inner feeling of exertion.
Use the descriptions in the table to help you assess what level you are running at. As you become fitter, you’ll be able to maintain a higher RPE for longer.
There’s also a kids’ version of the RPE
Rating of Perceived Exertion (RPE) for kids