Watch bands are measured and sold by width. The width is measured where the watch band connects to the watch. Measurements are taken in millimeters. There are 25.4 millimeters per inch. There, a spring is inserted through the band and into slots in the watch piece itself to hold firm. It is important to get the right width band so that it looks proper and fits the watch piece correctly. It is even more important to get the right sized pin so that the band remains attached and you do not lose your watch!

Metal bands are harder to match than leather bands, because there is the band itself, and the connecting pieces must fit just right also. These connecting pieces are not exactly standard, although many can interchangeable. Leather bands only need to be the right width and they will attach correctly. Also many people prefer to match the brand of the new band with the existing watch. You can also keep your existing clasp and put that on any other band. That will keep the logos matching with the watch itself.

It is harder to find bands by length, and often that is a determining factor for anyone with a larger sized wrist. This tends to be a larger problem for leather bands because they need to sit right after fastened. Aftermarket brands seem to do a better job at addressing the issue of watch band length.