If you are talking about life drawing in art, then you will get several suitable websites if you key in the words Proportion, Life Drawing, Art Life Studies and similar words. In general terms the body is usually splilt into eight sections to get the proportions correct. The head is the first eight, then the torso and legs are approximately the other three and four sections respectively, although some non-traditional artists might disagree.
If you are talking about the length a person's leg should be to be considered as attractive in model terms, then I haven't much of a clue, although I know the model Rachel Hunter is renowned for the length of her legs so maybe you could look it up on the web.