How To Measure Watch Band Loop. Band size is the combined length of the two straps. Otherwise, you will need to find the lug width (distance between the inside of the lugs on the watch head).
That extra length (again, on average, between 38 and 46 millimeters) is what allows one watch band to fit a broad range of wrists. Measure leather, only (do not include buckle), using an english ruler (remember, we are using inches to measure length). If you already have a leather band for the watch in question, you can check the back to see if it has a size imprint, shown in millimeters.
Measure your existing strap if you have an existing leather strap that fits, measure it to determine your required length.
Go to apple online store and find any solo loop band, click the “start your measurement” button. The same rule of thumb applies: What’s next?” enter the measurement you just took, and apple’s site will tell you which size is best. Add the three measurements together.