Dozens: Unit Conversion & Definition ― JustinTOOLs.com

A dozen is has twelve (12) items of something. The term goes back to duodecim, which means 12 in Latin. Humans might have started to count on a base 12 because there are approximately 12 cycles of the moon in one cycle of the sun. In other words, a solar year has 12 months. The first to have used the unit were probably the Mesopotamians.

12 dozen (144 items) are a gross. 12 gross (1728 items) are called a great gross. A great hundred is 120 or ten dozen (a dozen for each finger on both hands).