🪐 Astronomical Unit Distance Converter

Convert between astronomical units (AU) — the average Earth-Sun distance — and other distance units.

Value

Unit

The constants behind the conversion

Whatever unit you pick, the value is turned into astronomical units first and the other three are rebuilt from it:

1 AU        = 149,597,870.7 km   (exact, by definition)
1 light year = 9,460,730,472,580.8 km = 63,241.1 AU
1 km         = 0.62137119223733 miles

Enter 1 AU and you get 92,955,800 miles, 149,598,000 km and 1.5813e-5 light years. Neptune’s 30.07 AU comes back as 4,498,410,000 km. Going the other way, 1 light year is 63,241.1 AU. Figures print to six significant figures, and light years always use exponential notation because inside the solar system they are vanishingly small numbers.

What an AU actually is

It is a fixed length, not a measurement. The AU began as the mean Earth–Sun distance, but since 2012 it has been defined as exactly 149,597,870,700 metres. Earth’s real distance still swings from 0.983 AU in January to 1.017 AU in July.
It doubles as a clock. Light crosses one AU in 499 seconds, so sunlight is 8.32 minutes old when it reaches you and a signal to a probe at 5.2 AU takes 43 minutes each way.
Know when to switch units. AU suits the solar system, light years suit the stars. Proxima Centauri is 268,000 AU away, which is why nobody quotes it that way.

Miles here are statute miles, the ordinary road mile. Nautical miles are 15% longer and are not used for astronomical distance.

Frequently asked questions

How many miles is 1 AU?

92,955,807 miles, which the converter rounds to 92,955,800. The round 93 million miles you see in textbooks is that figure trimmed.

How many AU are in a light year?

63,241.1. Both constants are exact, so the ratio is exact too: divide 9,460,730,472,580.8 km by 149,597,870.7 km.

How far away is Pluto in AU?

Its orbit runs from 29.7 AU to 49.3 AU, averaging 39.5 AU. Type 39.5 and you get about 5.91 billion km, or 3.67 billion miles.