Adjusting a dog's collar to the proper size for his neck is crucial to his health and safety. If a dog's collar is too tight, it could irritate his skin, choke him and even cause harm to his larynx. If it is too loose, he could slip out of his collar and potentially be hit by a car or have an encounter with a wild animal such as a skunk, porcupine or wolf.
Measure Your Dog's Neck
Use a flexible tape measure to note your dog's neck size so you know which collar size will be appropriate. Measure the circumference of your dog's neck in the area where the collar will sit. Do not purchase a collar for the exact size of your dog's neck.
Use the Two Finger Rule
The Humane Society of the United States says a properly adjusted regular, flat collar, whether leather or fabric, should allow for two fingers to fit between a dog's collar and his neck. Place your middle and index fingers between the collar and neck. They should slide in easily and comfortably. If three or more fingers fit in the space, the collar is too loose. If only one finger fits, it is too tight.
Recheck the Collar Regularly
Test the adjustment of your dog's collar every two weeks. This is especially crucial for growing dogs, but it is also important for full grown dogs because their weights can fluctuate causing a need for collars to be tightened or loosened.
Transfer Your Dog's Tags
If you purchase a new collar for your dog, make sure it is adjusted for proper size with the two finger method, and then transfer his identification tag, his dog license and his rabies vaccination tag to the new collar.
For special use and aversive collars, consult the manufacturer for proper sizing and adjustment.