100 or one hundred (Roman numeral: C) is the natural number following 99 and preceding 101.

100 is the square of 10 (in scientific notation it is written as 10²). The standard SI prefix for a hundred is "hecto-".

100 is the basis of percentages (per centum meaning "by the hundred" in Latin), with 100% being a full amount.

100 is a Harshad number in decimal, and also in base-four, a base in-which it is also a self-descriptive number.

100 is the sum of the first nine prime numbers, from 2 through 23. It is also divisible by the number of primes below it, 25.

100 cannot be expressed as the difference between any integer and the total of coprimes below it, making it a noncototient.

100 has a reduced totient of 20, and an Euler totient of 40. A totient value of 100 is obtained from four numbers: 101, 125, 202, and 250.

100 can be expressed as a sum of some of its divisors, making it a semiperfect number. The geometric mean of its nine divisors is 10.