How many hours of sleep do dogs require a night?

My dog has been sleeping a lot lately (she is a golden retriever, if that has anything to do with sleeping hours) and I was wondering if anyone out there knew about how many hours dogs require of sleep a night. Thanks.

Adult dogs spend approximately half of their life sleeping, typically twelve hours each day and some breeds may sleep as much as 18 hours per day! Dogs may sleep out of boredom, but they also know when to be awake and aware of their surroundings and next thing you know, they’re back to taking a nap. Age plays a factor as well; as you can imagine, older dogs sleep more than younger dogs do.