I was not expecting to see a full-height picture of Fillyjonk, yet there it was, with the following disclaimer regarding skirt length:
This is as short as I will EVER go in a dress, even this makes me a little uncomfortable.
Which is more or less consistent with the observations I’ve been making since approximately age ten, when I first noticed things like this: just about every woman has a sense of “This far up, but no farther.” I have since come up with a rule of, well, not exactly thumb:
[A] hemline should be low enough to conceal anything that might be better off concealed.
Still, this comes off as unsatisfactorily subjective, so I went hunting about, and turned up a rule perhaps more universally applicable:
The short answer is that you want your hemline to hit a relatively small part of your leg. If you look at the natural shape of most women’s legs, the widest part is the mid thigh and mid calf while the most narrow part is the knee and ankle.
This makes sense, because the eye (or at least my eye) is inevitably drawn to that intersection of hem and leg, and the first rule of fashion is always to draw the eye to what you want to be noticed, and away from anything you’d just as soon nobody noticed. Bad hair day? Either shorten your skirt, or find your deepest V-neck top. No one will say a word about your coif.
The really short dresses, of course, are best left to women who don’t have a whole lot of thigh taper and who have no qualms about letting you know about it. You may know someone like that. I don’t. (I know someone who qualifies on the first part, but at age 70 she’s not about to show off.)