An exametre (American spelling: exameter, symbol: Em) is a unit of length equal to 10¹⁸ metres.

Exametres could be used for measuring interstellar distances, but astronomers have been long accustomed to use light-years and parsecs instead.

• 1 Em is equal to 105.7 light-years or 32.41 parsecs
• the distance to Betelgeuse is 4 Em
• the distance to the center of our Galaxy is 265 Em
• light travels the distance of 1 Em in 105.7 years

petametre << exametre << zettametre

See also

• 1 E18 m
• SI
• SI prefix
• Orders of magnitude