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13 objects with sizes in the gigameter order of magnitude
1 gigametre =
SI units
1.000×10^6 km 1.000×10^9 m
Astronomical units
6.685×10^−3 AU 105.7×10^−9 ly
US customary / Imperial units
621.4×10^3 mi 3.281×10^9 ft

The gigametre (official spelling used by the International Bureau of Weights and Measures;[1] SI symbol: Gm) or gigameter (American spelling) is a unit of length in the metric system, equal to one billion metres, the SI base unit of length, hence to 1,000,000 km or approximately 621,370 miles.

Gigametres (from the Greek words gigas = giant and metro = count/measure) are rarely seen in practical use. They are too big for any terrestrial lengths, and gigametre distances in astronomy (e.g. a planet's distance from its star) are usually given in astronomical units (AU) or in (millions of) kilometres.

See also[edit]


  1. ^ "Definition of the metre". BIPM. Retrieved 26 March 2014. 
  2. ^ Emilio, Marcelo; Kuhn, Jeff R.; Bush, Rock I.; Scholl, Isabelle F. (March 5, 2012), "Measuring the Solar Radius from Space during the 2003 and 2006 Mercury Transits", arXiv, retrieved March 28, 2012