Baker’s Dozen

You use the term ‘Baker’s Dozen’ to refer to thirteen of something.

Example of use: “I’ll take a baker’s dozen of those donuts, please.”

Interesting fact

"Throughout history, bakers have been subject to strict penalties for cheating their clients. To prevent accusations from flying, they often included a little extra, giving 13 loaves if 12 were ordered.  The practice was common during the 12th century and probably originated before then."