I have noticed that my dog sleeps quite a lot. Below I post a photo of her - she looks sleepy in it :-)
People sleep on average about 8-9 hours a day and are active during the day. Dogs do not have the same pattern - they catch several short naps aparat from the night's sleep. Counting little naps and longer snoozes,most dogs sleep about fourteen hours a day. Large breeds generally spend a lot of time sleeping even up to 18 hours a day. Smaller dogs need less time to sleep (but Puppies might also get 18 hours a day of sleep cause they are babies)
Amount of sleep that your dog has depends also on the amount of daily activities.
Dogs also adjust their sleeping patterns to be able to be alert each time that something is going on.
Here is an intersting article How Long Dogs Sleep on Average