The case size of a watch is measured as the diameter of the watch, not including the crown or the lugs.
US QUARTER DOLLAR
Measure the circumference of your wrist to find the watch that’s right for you.
Measuring your wrist for your Water Cuff
The size of a watch strap’s width is determined by the portion of the strap that connects to the watch lugs, otherwise known as the ‘lug width’.