Well, this part is a bit challenging! But, if your dog does not settle for less, you can get an idea that the collar may be disturbing him.  The best way to check whether a collar is a perfect fit or not is by using the two-finger rule. If you cannot slide your finger underneath the collar, it means the collar is too restricting. On the other hand, if you can do so, congratulations, the collar fits! If you can fit more than two fingers in another scenario, it means the collar is too loose. Therefore, consider all conditions when determining the perfect fit.