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AU to Kilometers Converter

Enter a value and pick a direction to convert between AU and kilometers.

Result

227,388,763.46 km
1 AU = 149,597,870.70 km
1.520000 AU

How it is calculated

The conversion uses the fixed value 1 AU = 149,597,870.7 km. In the AU to km direction it multiplies: km = AU × 149,597,870.7. In the km to AU direction it divides: AU = km ÷ 149,597,870.7. Kilometre results are shown with two decimals and AU results with six, because AU values are small for everyday distances. The tool also prints the rate and the entered value converted back, as a check. If you pick km to AU, enter the number in kilometres. Any direction value other than km to AU is treated as AU to km. Negative values return no result, since a distance cannot be negative.

Worked example

Mars orbits at about 1.52 AU from the Sun. Choose the AU to km direction and multiply: 1.52 × 149,597,870.7 = 227,388,763.46 km. The check line converts that back to 1.520000 AU. In the other direction, the Moon's average distance of 384,400 km divided by 149,597,870.7 gives 0.002570 AU, which shows why AU is awkward for distances inside the Earth-Moon system.

Try this example →

Common mistakes

  • Leaving the direction on AU to km when the number is already in kilometres, which inflates the value by about 150 million times.
  • Confusing AU with a light year; one light year is about 63,000 AU, so the units are very far apart.
  • Reading the six-decimal AU result as exact to six places for a distance that is only known approximately, such as an orbit that varies between nearest and farthest approach.
  • Treating Earth-Sun distance as constant; 1 AU is a fixed definition, while the actual distance changes through the year.
  • Entering a negative value to express direction; the tool accepts only distances of zero or more.

About this calculator

The astronomical unit (AU) is defined as exactly 149,597,870.7 kilometers — roughly the average Earth-Sun distance — and serves as the standard yardstick for measuring distances within our solar system, where expressing everything in kilometers would produce unwieldy numbers.

Mars orbits at about 1.52 AU from the Sun (227.9 million km), and Neptune sits at roughly 30.1 AU (4.5 billion km) — numbers that stay compact and easy to compare in AU but become hard to parse in raw kilometers. This converter switches between the two in either direction with a simple multiplication or division by the fixed 149,597,870.7 km/AU constant.

Astronomy students, science communicators, and space enthusiasts use AU when discussing planetary distances or spacecraft trajectories, then convert to kilometers when a calculation or comparison needs metric units instead.

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Comments (1)

  • Editorial team

    A useful way to feel the scale is light travel time. Light covers 1 AU in about 499 seconds, a little over 8 minutes, and a signal to something at 30.1 AU takes roughly 4 hours 10 minutes one way. Divide the kilometre figure the tool gives by 299,792 km/s to get the same thing in seconds. Orbits are ellipses, so a planet's AU figure here is an average. Which object's distance are you converting?

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