45th is the ordinal form of the number 45. 45th or Forty-fifth may also refer to:
A fraction, , equal to one of 45 equal parts
Geography 45th meridian east, a line of longitude 45th meridian west, a line of longitude 45th parallel north, a circle of latitude 45th parallel south, a circle of latitude 45th Street station (disambiguation)
Military 45th Army 45th Brigade (disambiguation) 45th Division (disambiguation) 45th Regiment (disambiguation) 45th Squadron (disambiguation)
Other 45th century 45th century BC
See also 45 (disambiguation)