Most of my UKs hit just slightly below mid-knee.

My favorite UK hits slightly below the knee which is great because I wear it when I teach CPR and the extra length keeps my bits covered when I'm crawling around on the floor where people are laying down.

I've recently ordered a tartan kilt (from our Ursa Major) and I went to some trouble to make sure it was the tradition mid-knee length. Since the intent is to have a more traditional look (including sporran and kilt hose), I'm going for a more traditional length.

But I won't be wearing it to teach CPR.