I think it's a matter of comfort, modesty, and all about the knee. My 8 yarder falls about mid-knee. It is my longest kilt and I think (being extremely subjective here) it has a slightly more formal look. I have a casual and box pleat on order that are tailored to be 1/2" higher to the top of the knee or there abouts. It seems to me that more "contemporary" stylings tend to be a little longer than mid knee (I would find that uncomfortable and not within traditional standards). When you're measuring, I would go with the length that you feel most "at home" with. Modern/contemporary length tends to fall longer, I think. Long-standing practice is mid-knee and shorter. Now, because I have a public job and am often sitting on stage/platform, I like a little more to work with, if you know what I mean!