astronomical unit

astronomical unit

Non-SI unit accepted for use with SI
Name Symbol Quantity Value in SI units
astronomical unit au length 149 597 870 700 m
149.597 870 7 Gm


The astronomical unit, symbol au, is a non-SI unit of length accepted for use with the SI.

One astronomical unit is equal to 149 597 870 700 m, or approximately 150 gigametres.

The astronomical unit is approximately equal to the average distance from the Earth to the Sun. It is used primarily in the field of astronomy for measuring distances within the Solar System, or interplanetary distances around other stars.

Examples of distances of planets from the Sun
Name Distance in au Distance in SI units
Mercury 0.387 58 Gm
Venus 0.723 108 Gm
Earth 1 150 Gm
Mars 1.52 228 Gm
Jupiter 5.20 778 Gm
Saturn 9.54 1427 Gm
Uranus 19.2 2871 Gm
Neptune 30.1 4495 Gm