|This article does not cite any references or sources. (December 2009)|
|1,000.00 km||1.000×106 m|
|6.685×10−6 AU||105.7×10−12 ly|
|US customary / Imperial units|
|621.37 mi||3.281×106 ft|
A megametre (American spelling: megameter, symbol Mm) is a unit of length in the metric system, equal to one million metres, the SI base unit of length, hence to 1,000 km or approximately 621.37 miles.
Megametres (from the Greek words megas = big and metro = count/measure) are rarely seen in practical use, e.g. "5000 km" is much more common than "5 Mm". The symbol (Mm) can also be confused with millimetres (mm) and care should be taken to use the correct capitalisation when using such symbols. Megametres are also occasionally found in science fiction.
- The Earth's polar circumference is 39.94 Mm. (It was exactly 40 Mm from 1791 to 1875, but the definition of the metre was changed; see metre).
- The distance from Amsterdam to Marseille is approximately 1 Mm.
- The Earth's equatorial diameter is 12.76 Mm.
- The mean distance from the Earth to the Moon is 384.4 Mm.
- Jupiter's equatorial diameter is 143 Mm.
- Quebec province's total area is 1.542 Mm2.
- The Speed of light is approximately 299.792 Mm/s.
 See also
- 1 E+6 m
- SI prefix
- Metric system
- Orders of magnitude (length)
- Conversion of units, for comparison with other units of length
- Light year