**Things that come in groups of 12 are called dozens.** The word "dozen" is derived from "douzaine," the French word for "exactly 12." This French word, in turn, is derived from the Latin word for twelve, "duodecim."

A dozen has long been a convenient measuring number. Unlike the number 10, 12 is evenly divisible by most single-digit numbers: 1, 2, 3, 4 and 6. Thus, it is easy to sell items by the dozen or by a fraction of a dozen. The custom of counting in dozens or multiples of dozens probably originated in Mesopotamia. Their sexagesimal system, using 60 as a base number, used the mathematical advantages of 12 and added the 5 and 10 as divisors.

A dozen dozens, or 144, is termed a "gross." It is also of French origin, specifically "gross douzaine" or "large dozen." A "great gross" is a dozen gross. A "small gross" is 10 dozen.

A baker's dozen, or 13, has a somewhat different origin. Medieval bakers often sold rolls and other small baked goods in dozens. However, they risked fines if the items sold did not meet a statutory weight. Therefore, they would often put an extra roll into a batch of a dozen to ensure it weighed enough. A baker's dozen may also be called a "long dozen."