Determining if a watch will suit your wrist

Found a vintage watch that I like but I wasn't sure if it would fit my wrist. Got the brilliant idea of drawing a circle the size of the watch on my wrist  End result is that I have a lopsided circle on my wrist and I'm no closer to determining if it will fit or not. My question for you is how do you guys determine if a watch you're interested in will fit your wrist. Also how had the same brilliant idea I had and went through with it?