The amount of time spent napping varies from dog to dog and depends on the dog's age and personality. Counting little naps and longer snoozes, most puppies sleep from 18 to 20 hours a day. As your puppy ages, he will sleep less. Adult dogs sleep about fourteen hours a day. The various breeds of dogs also seem to have different sleep requirements. Some very large breeds of dogs, like Newfoundlands, Saint Bernards, and mastiffs, often spend a great deal of their lives sleeping – perhaps up to sixteen or even eighteen hours a day even as adults.