12 (number)

12 is a natural number that comes after 11 and before 13. In Somali it is called "laba iyo toban" (literally two and ten). It is written as 12 in decimal notation, XII in Roman numerals, and 1100 in binary.

12 is widely used in measurement and counting because it has many divisors relative to its value. It is divisible by 1, 2, 3, 4, 6, and 12—making it suitable for division into two, three, or four equal parts.

Mathematical properties

12 is a composite number, meaning it has divisors other than 1 and itself. It is a highly composite number, as no smaller number has more divisors. The sum of its proper divisors—1+2+3+4+6—is 16, which is greater than 12; therefore it is an abundant number. Its prime factorization is 2² × 3.

In geometry, a polygon with twelve sides is called a dodecagon. A circle can be divided into twelve equal parts, as can triangles and squares, making 12 a practical base for geometric division.

The duodecimal system

A counting system with base 12 is called duodecimal. Proponents of this system argue that fractions such as one-third and one-quarter become whole numbers, whereas in base ten they do not. The sexagesimal system used in ancient Babylon, still employed for measuring time and angles, derives from the combination of 12 and 5.

Use in daily life

A year is divided into twelve months, a day into twenty-four hours (two periods of twelve), and the lunar cycle is approximately twelve months per year. In commerce, a group of twelve is called a dozen, still used for counting eggs and other goods. Earlier measurement systems, such as those using inches, employed division by twelve.