Your rest days are going to be a result of a number of different factors. There are many many people that can exercise at varying intensities for days on end in a row with no ill effects, but others that absolutely require rest days. The basic trick is getting to know your own body and how it is reacting to the exercise.
To use your example, you are exercising at what I personally would term a fairly light intensity. This is something that could be repeated day after day without ill effect, at least in my personal situation. However, if I upped the ante and added in more distance, or intervals or other high intensity variations, then I might need a rest day here and there.
Unfortunately, as alluded to in the comments, it's very much dependent on your own training, your own adaptation and your own tolerance for fatigue. I can give you the personal guideline that if I head out the door for a workout and within 5ish minutes I just know I'm "not feeling it", I will bag the workout and take a rest day. The best answer you're going to get is "it depends".