- Roman numerals: L
- decimal or Arabic notation: 50
It is the smallest number that can be written as the sum of two squares in two distinct ways: 50 = 12 + 72 = 52 + 52. It is also the sum of three squares, 50 = 32 + 42 + 52.
Fifty is also:
- The atomic number of tin.
- The number of states in the USA (since 1959, still true in 2004)
- A calibre of ammunition (0.50 inches: see .50 BMG)
- In millimeters, the focal length of the normal lens in 35mm photography.
- the percentage equivalent to one half, so that "fifty-fifty" is commonly used for something divided equally in half, or an event of probability one half
- In U.S. dollars, the denomination of the Federal Reserve note with with Ulysses S. Grant's portrait, the denomination of the savings bond with George Washington's portrait, and the denomination of treasury bonds with Thomas Jefferson's portrait.
- In cents of the U.S. dollar, the denomination of the coin with John F. Kennedy's portrait.
- In years of marriage, the gold wedding anniversary.
This article is about the number. For the year AD 50, see 50.