My first kilt (tank) was measured for me by a kilt maker in the shop of Thomas Gordon and Sons in Glasgow. It falls (when worn properly at the right hight) to right at the bottom of my knee, and is the longest kilt I own.

When ever I have sold UK's I always said middle of the knee or shorter, but that it also depended on what the customer wanted. Many opted for slightly longer. Why, because the bottom of the knee is where most shorts these days also hit, and guys are comfortable with that length.

Adam