Convert km to astronomical unit

One kilometer equals 0.000000006685 astronomical units. To convert any number of kilometers to astronomical units, multiply by 0.000000006685.

The converter above works in both directions and updates as you type. Below you will find the formula, a worked example and a reference table of common values.

Length conversions come up wherever a measurement crosses a border: a height given in feet and inches on a form that wants centimetres, a running distance recorded in kilometres and compared against miles, a component specified in millimetres and ordered from a supplier working in inches. The conversions themselves are exact — the inch, foot, yard and mile have all been defined in metric terms since 1959 — so any discrepancy comes from rounding, not from the units disagreeing.

km to astronomical unit formula

To go the other way, use kilometer = astronomical unit ÷ 0.000000006685.

About these units

The kilometre is a thousand metres, and the standard road-distance unit in every country except the United States, the United Kingdom and a handful of others.

The astronomical unit is the mean Earth–Sun distance, fixed since 2012 at exactly 149,597,870,700 metres. It is the natural ruler for anything inside a solar system.

Kilometer is also written kilometre, kilometres, kilometers and kms. Astronomical Unit is also written astronomical units and a.u..

Sources

1. International Astronomical Union, Resolution B2 (2012), XXVIII General Assembly — the astronomical unit as exactly 149,597,870,700 m, and the Julian year of 365.25 days from which the light year and parsec follow.