How to size your dog for the fur saver: Please measure the circumference of your dog's neck and head in the widest place. Compare neck and head sizes and add 1-2 inches to bigger size to determine an appropriate collar length. For Example: your dogs neck around 20 inches and head around (in the widest part) 22 inches. You should add 1-2 inches to bigger - head size in this case and choose 23 or 24 inches size collar