You’ll need to start with a cloth measuring tape. Wrap the tape around your dog’s neck positioned where his\her collar sits. If you don’t have a cloth measuring tape a piece of string and ruler would work just as well. After you’ve got your measurement you’ll add two inches, this will be your dog’s collar size. Check the collars fit. You want it to be snug but with enough room to slip two fingers in between your dog’s neck and the collar. The width should be proportionate to your dog’s size.