From personal experience, I would suggest going with a hip size that is 2 to 4" larger than your waist size, even if it's incorrect. I imagine what is happening, is that your gut (sorry if that's offensive, that's what mine is, a gut ) hangs out making it larger than your hip size. However, you want the kilt to hang nicely, so go with a larger number. Just make sure that you state that to your kilt maker.

Mike