An astronomical unit is the mean Earth-Sun distance.
Astronomical units to Kilometers Converter — AU to km
Convert Astronomical unit (AU) to Kilometer (km) using the exact conversion factor (1 astronomical unit = 149,597,870.7 kilometer). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Astronomical units to Kilometers converter
Converter
Astronomy Converter
Convert astronomical length, mass, time, and distance units by compatible family.
Context values
Some unit families need one extra value for a physically accurate result.
Kilometer is 1000 meter units.
Result = input x 1.49597871e+11 / 1000.
Distance units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Astronomical units to Kilometers
Astronomical unit and Kilometer both describe astronomical distances at very different scales — one for measuring within our solar system, the other for the distances between stars — and converting between them helps put the scale of space into perspective. Astronomical unit is typically associated with used internationally in astronomy for solar-system-scale distances., while Kilometer is typically associated with standard road, distance, and mapping unit in nearly every country except the United States.
Formula
kilometers = astronomical units × 149597870.7
This factor comes from each unit's defined relationship to the category's base unit: 1 astronomical unit equals 149597870700 base units, and 1 kilometer equals 1000 base units, so dividing one by the other gives the direct astronomical unit-to-kilometer factor of 149597870.7.
Simple example
1 AU × 149597870.7 = 149,597,870.7 km
1 astronomical unit = 149,597,870.7 kilometers.
Real-world example
4.24 AU × 149597870.7 = 634,294,971.8 km
4.24 astronomical units = 634,294,971.8 kilometers.
Conversion table
| Astronomical unit (AU) | Kilometer (km) |
|---|---|
| 1 AU | 149,597,870.7 km |
| 4.24 AU | 634,294,971.8 km |
| 10 AU | 1,495,978,707 km |
| 100 AU | 14,959,787,070 km |
| 1,000 AU | 149,597,870,700 km |
| 1,000,000 AU | 1.495979e+14 km |
Reverse conversion: Kilometer to Astronomical unit
1 km × 6.684587e-9 = 6.684587e-9 AU
1 kilometer = 6.684587e-9 astronomical units.
astronomical units = kilometers × 6.684587e-9
For a page dedicated to this direction, see Kilometer to Astronomical unit.
Astronomical unit vs. Kilometer
| Aspect | Astronomical unit | Kilometer |
|---|---|---|
| Family | Non-SI unit accepted for use with SI (astronomical) | SI derived (metric prefix) unit |
| Typical use | Measuring distances within the solar system (planetary orbits) | Road signage, speed limits, and vehicle odometers outside the US |
| Where it's used | Used internationally in astronomy for solar-system-scale distances. | Standard road, distance, and mapping unit in nearly every country except the United States |
Understanding the Astronomical unit
Astronomical unit (AU) measures distance. The astronomical unit is defined as exactly 149,597,870,700 meters, close to the average Earth-Sun distance. It is classified as a Non-SI unit accepted for use with SI (astronomical).
Where it's used: Used internationally in astronomy for solar-system-scale distances.
Uses of the Astronomical unit today
- Measuring distances within the solar system (planetary orbits)
- Astronomical calculations and spacecraft navigation
- Popular science communication about the solar system
History of the Astronomical unit
The astronomical unit originated from 17th-19th century attempts to measure the Earth-Sun distance, refined over time using transits of Venus and later radar and spacecraft ranging.
In 2012, the International Astronomical Union fixed the AU at exactly 149,597,870,700 meters, replacing its earlier definition (tied to gravitational calculations) with a simple fixed distance, independent of the slightly-variable actual Earth-Sun distance.
Historical origin. Astronomical unit was not the invention of a single named person; it developed through the process described above.
Understanding the Kilometer
Kilometer (km) measures distance. A kilometer is 1,000 meters — the meter is the SI base unit of length. It is classified as a SI derived (metric prefix) unit.
Where it's used: Standard road, distance, and mapping unit in nearly every country except the United States
Uses of the Kilometer today
- Road signage, speed limits, and vehicle odometers outside the US
- Geographic and mapping distances
- Endurance sports (marathons are measured in kilometers internationally, though the marathon distance itself is a fixed value in both systems)
History of the Kilometer
The meter was defined during the French Revolutionary metric reforms as one ten-millionth of the distance from the North Pole to the Equator along a meridian through Paris. 'Kilo-' is simply the SI prefix for 1,000, making the kilometer a direct decimal multiple.
The meter itself has been redefined several times as measurement precision improved — from a physical platinum-iridium bar (1889) to a krypton-86 wavelength (1960) to its current definition (1983) as the distance light travels in a fixed fraction of a second.
Historical origin. Kilometer was not the invention of a single named person; it developed through the process described above.
Astronomical unit — sources
- IAU Resolution B2 (2012) — Fixes the astronomical unit at exactly 149,597,870,700 meters.
Kilometer — sources
- BIPM — The metre (SI base unit) — Current definition and history of the meter.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many kilometers are in 1 astronomical unit?
1 astronomical unit equals 149,597,870.7 kilometers, using the exact defined conversion factor rather than an estimate.
How do I convert astronomical unit to kilometer?
Multiply the astronomical unit value by 149597870.7. The converter above does this instantly to whatever precision you set.
How do I convert kilometer back to astronomical unit?
Use the reverse factor: 1 kilometer equals 6.684587e-9 astronomical units. You can also use the swap control in the converter above to flip the direction instantly.
What is a astronomical unit?
Astronomical unit (AU) measures distance. The astronomical unit is defined as exactly 149,597,870,700 meters, close to the average Earth-Sun distance. It is classified as a Non-SI unit accepted for use with SI (astronomical).
What is a kilometer?
Kilometer (km) measures distance. A kilometer is 1,000 meters — the meter is the SI base unit of length. It is classified as a SI derived (metric prefix) unit.
Is the astronomical unit to kilometer conversion exact?
Yes. The astronomical unit is defined as exactly 149,597,870,700 meters, close to the average Earth-Sun distance. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
Where is the astronomical unit still used today?
Used internationally in astronomy for solar-system-scale distances.