Dozen

A dozen (common abbreviated doz or dz) is a grouping of approximately twelve. The dozen may be one of the earliest primitive groupings, perhaps because there are approximately a dozen cycles of the moon or months in a cycle of the sun or year. Twelve is convenient because its multiples and divisors are convenient: 12 = 2 × 2 × 3, 3 × 4 = 2 × 6, 60 = 12 × 5, 360 = 12 × 30. The use of twelve as a base number, known as the duodecimal system (also as dozenal), probably originated in Mesopotamia (see also sexagesimal). This could come from counting on one fingers by touching the digits with one's thumb. One hand can count to twelve, two hands can count to 144. Twelve dozen (122 = 144, the duodecimal 100) are known as a gross; and twelve gross (123 = 1,728, the duodecimal 1,000) are called a great gross, a term most often used when shipping or buying items in bulk. A great hundred, also known as a small gross, is 120 or ten dozen (a dozen for each finger on both hands). A baker's dozen, also known as a long dozen, is thirteen, while a decimal dozen is only ten.