Becky, in my experience, I have noticed that when the follicles get to be about 20 mm, is when you can feel them when palpating. I have felt them before at 18 mm, but not very often. At 20 mm when I can feel them, following the 5 mm/week rule, they should ovulate about four weeks after you feel them the first time. So far it is a opretty good guide, but always has exceptions.