A gigametre (American spelling: gigameter, symbol: Gm) is a unit of length equal to 10⁹ metres. Its customary equivalent is 621,371 miles.

Gigametres are almost never seen in practical use, because they are too big for any terrestrial application, and astronomers have been long accustomed to use millions of kilometers and astronomical units (AU) instead.

• 1 AU is equal to 149.6 Gm
• diameter of the Sun is 1.4 Gm
• mean radius of Mercury's orbit is 57.9 Gm
• mean radius of Jupiter's orbit is 778.4 Gm
• mean radius of Ganymede's orbit (around Jupiter) is 1.07 Gm
• light travels the distance of 1 Gm in approximately 3.34 s

megametre << gigametre << terametre

See also

• 1 E9 m
• SI
• SI prefix
• Orders of magnitude
• light year
• parsec