a long dozen

a long dozen

Thirteen, i.e., one more than a usual dozen (12). When Jacob went to the bakery to buy doughnuts for the office, he made sure to get a long dozen so he could have one to himself on the way to work. They have a sale on at the moment—a long dozen onion and garlic bagels for just $8.
See also: dozen, long
Farlex Dictionary of Idioms.

long dozen

n. thirteen; a baker’s dozen. They used to give you a long dozen in that bakery.
See also: dozen, long
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • long dozen
  • a baker's dozen
  • baker
  • baker's dozen
  • a banker's dozen
  • banker
  • baker's half dozen
  • half a dozen
  • by the dozen(s)
  • by the dozens