Collar Size: SafeCalm collars are one-size-fits-all, and only determined by your dog's weight. For Example: if your dog weighs 35 LBS, it can wear a Large SafeCalm collar. It is not necessary to measure your dog's neck or snout. The XXL SafeCalm collar is not for regular big dogs like big Shepherds or big Pit bulls, an XL will work great. XXL collars are only for huge dogs: St. Bernards, Great Danes, or any dog over 75 LBS with an obvious huge neck, snout or both.