A baker’s dozen traditionally includes thirteen doughnuts.
The phrase “baker’s dozen” means thirteen items rather than the ordinary dozen of twelve. Bakers historically used the extra item as a safeguard against selling underweight goods, since loaves and other products could vary slightly in size. Giving thirteen for the price of twelve helped ensure that a customer received the promised quantity or weight.
The expression is older than modern doughnut chains and applies to many baked goods, including rolls, buns, and pastries. Doughnuts are a familiar modern example because they are commonly sold by the dozen.
A baker’s dozen is not the same as a “long dozen,” which can refer to thirteen in some contexts but is less specifically tied to baking. The standard arithmetic meaning of a dozen remains twelve; the extra item exists only in the traditional commercial phrase.