Kilometer is 1000 meter units.
Kilometers to Astronomical units Converter — km to AU
Convert Kilometer (km) to Astronomical unit (AU) using the exact conversion factor (1 kilometer = 6.684587e-9 astronomical unit). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Kilometers to Astronomical units 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.
An astronomical unit is the mean Earth-Sun distance.
Result = input x 1000 / 1.49597871e+11.
Distance units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Kilometers to Astronomical units
Kilometer and Astronomical unit 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. Kilometer is typically associated with standard road, distance, and mapping unit in nearly every country except the United States, while Astronomical unit is typically associated with used internationally in astronomy for solar-system-scale distances..
Formula
astronomical units = kilometers × 6.684587e-9
This factor comes from each unit's defined relationship to the category's base unit: 1 kilometer equals 1000 base units, and 1 astronomical unit equals 149597870700 base units, so dividing one by the other gives the direct kilometer-to-astronomical unit factor of 6.684587e-9.
Simple example
1 km × 6.684587e-9 = 6.684587e-9 AU
1 kilometer = 6.684587e-9 astronomical units.
Real-world example
4.24 km × 6.684587e-9 = 2.834265e-8 AU
4.24 kilometers = 2.834265e-8 astronomical units.
Conversion table
| Kilometer (km) | Astronomical unit (AU) |
|---|---|
| 1 km | 6.684587e-9 AU |
| 4.24 km | 2.834265e-8 AU |
| 10 km | 6.684587e-8 AU |
| 100 km | 6.684587e-7 AU |
| 1,000 km | 0.0000066846 AU |
| 1,000,000 km | 0.0066845871 AU |
Reverse conversion: Astronomical unit to Kilometer
6.684587e-9 AU × 149597870.7 = 0.9999999817 km
6.684587e-9 astronomical units = 0.9999999817 kilometers.
kilometers = astronomical units × 149597870.7
For a page dedicated to this direction, see Astronomical unit to Kilometer.
Kilometer vs. Astronomical unit
| Aspect | Kilometer | Astronomical unit |
|---|---|---|
| Family | SI derived (metric prefix) unit | Non-SI unit accepted for use with SI (astronomical) |
| Typical use | Road signage, speed limits, and vehicle odometers outside the US | Measuring distances within the solar system (planetary orbits) |
| Where it's used | Standard road, distance, and mapping unit in nearly every country except the United States | Used internationally in astronomy for solar-system-scale distances. |
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.
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.
Kilometer — sources
- BIPM — The metre (SI base unit) — Current definition and history of the meter.
Astronomical unit — sources
- IAU Resolution B2 (2012) — Fixes the astronomical unit at exactly 149,597,870,700 meters.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many astronomical units are in 1 kilometer?
1 kilometer equals 6.684587e-9 astronomical units, using the exact defined conversion factor rather than an estimate.
How do I convert kilometer to astronomical unit?
Multiply the kilometer value by 6.684587e-9. The converter above does this instantly to whatever precision you set.
How do I convert astronomical unit back to kilometer?
Use the reverse factor: 1 astronomical unit equals 149,597,870.7 kilometers. You can also use the swap control in the converter above to flip the direction instantly.
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.
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).
Is the kilometer to astronomical unit 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 kilometer still used today?
Standard road, distance, and mapping unit in nearly every country except the United States