Paw Brothers Premium Nylon Dog Muzzles are a safety must-have for handlers, groomers, vets and other pet professionals. Size 0 (Tiny) accommodates 4"- 4.5" To measure your dogs muzzle wrap a length of tape around the muzzle, just above the nose. Place your index finger between tape and muzzle making sure that the tape is loose enough to slide around the muzzle. Measure tape and choose closest size. It is better to have a fit that is slightly loose than to be too tight. Your dog needs to have free tongue movement to pant and to lap water.