Exercise intensity is important to gauge, because it can tell you whether you are working too hard, or not working hard enough! One common tool to do this is the “Rating of Perceived Exertion” scale (RPE for short).
No two runs are identical – factors such as: weather; terrain; tiredness/motivation; etc. will all influence the amount of effort required during exercise.
There are numerous versions of the scale – the one below is based on Matt Fitzgerald’s book, “80/20 Running”, and closely aligns with Strava’s Pace Zones.