40th is the ordinal form of the number 40. 40th or Fortieth may also refer to:
A fraction, , equal to one of 40 equal parts
Geography 40th meridian east, a line of longitude 40th meridian west, a line of longitude 40th parallel north, a circle of latitude 40th parallel south, a circle of latitude 40th Street (disambiguation)
Military 40th Battalion (disambiguation) 40th Brigade (disambiguation) 40th Division (disambiguation) 40th Regiment (disambiguation) 40th Squadron (disambiguation)
Other 40th century 40th century BC
See also 40 (disambiguation) The Fortieth Door, 1924 American adventure film serial