Forty-five (45, XLV) is the natural number following forty-four and followed by forty-six. It is a triangular number.

Its divisors are 3, 9, 15 and 45. Its prime factorization is

See also: forty
45 is also:

  • The atomic number of rhodium.
  • The total of books in the Old Testament of the Holy Bible in the Catholic version if the Book of Lamentations is considered part of the Book of Jeremiah.
  • In years of marriage, the sapphire wedding anniversary.
  • In reference to vinyl records, 45 refers to a type of record by its revolution speed of 45 revolutions per minute (rpm). This record disc was usually about 1/2 the circumference of a full record, with a larger central spindle, and contained one song on each side which resulted in calling such records singles.
Originally the 45 RPM record was introduced as a longer play version of the 78 RPM discs. The first 45 RPM records were monaural with recordings on both sides of the Disc. Produced in several sizes, the 7" large hole version became the most popular. As stereo recordings became popular in the 1950s, most all of the newer 45 RPM records were recorded in Stereo.

See: 78, LP and 33.
  • The caliber of some handguns.
  • a card game: Forty-five
  • The code for international direct dial phone calls to Denmark.
  • For the year 45 AD, see 45.