An astronomical unit is the mean Earth-Sun distance.
Astronomical units to Millimeters Converter — AU to mm
Convert Astronomical unit (AU) to Millimeter (mm) using the exact conversion factor (1 astronomical unit = 1.495979e+14 millimeter). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Astronomical units to Millimeters converter
Converter
Length Converter
Convert SI, imperial, US customary, astronomical, scientific, and historical length units.
Context values
Some unit families need one extra value for a physically accurate result.
Millimeter is 0.001 meter units.
Result = input x 1.49597871e+11 / 0.001.
Length uses the meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Astronomical units to Millimeters
Astronomical unit and Millimeter both measure length. Astronomical unit is typically associated with used internationally in astronomy for solar-system-scale distances., while Millimeter is typically associated with standard small/precision length unit worldwide, including in US engineering and manufacturing.
Formula
millimeters = astronomical units × 1.495979e+14
This factor comes from each unit's defined relationship to the category's base unit: 1 astronomical unit equals 149597870700 base units, and 1 millimeter equals 0.001 base units, so dividing one by the other gives the direct astronomical unit-to-millimeter factor of 1.495979e+14.
Simple example
1 AU × 1.495979e+14 = 1.495979e+14 mm
1 astronomical unit = 1.495979e+14 millimeters.
Real-world example
10 AU × 1.495979e+14 = 1.495979e+15 mm
10 astronomical units = 1.495979e+15 millimeters.
Conversion table
| Astronomical unit (AU) | Millimeter (mm) |
|---|---|
| 1 AU | 1.495979e+14 mm |
| 5 AU | 7.479894e+14 mm |
| 10 AU | 1.495979e+15 mm |
| 21.0975 AU | 3.156141e+15 mm |
| 42.195 AU | 6.312282e+15 mm |
| 100 AU | 1.495979e+16 mm |
Reverse conversion: Millimeter to Astronomical unit
1.495979e+14 mm × 6.684587e-15 = 1.000000196 AU
1.495979e+14 millimeters = 1.000000196 astronomical units.
astronomical units = millimeters × 6.684587e-15
For a page dedicated to this direction, see Millimeter to Astronomical unit.
Astronomical unit vs. Millimeter
| Aspect | Astronomical unit | Millimeter |
|---|---|---|
| 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) | Engineering drawings and manufacturing tolerances worldwide (including in the US) |
| Where it's used | Used internationally in astronomy for solar-system-scale distances. | Standard small/precision length unit worldwide, including in US engineering and manufacturing |
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 Millimeter
Millimeter (mm) measures distance. A millimeter is one-thousandth of a meter. It is classified as a SI derived (metric prefix) unit.
Where it's used: Standard small/precision length unit worldwide, including in US engineering and manufacturing
Uses of the Millimeter today
- Engineering drawings and manufacturing tolerances worldwide (including in the US)
- Rainfall measurement in most countries
- Small-scale everyday measurement (screen sizes, hardware)
History of the Millimeter
The millimeter follows from the meter via the 'milli-' SI prefix (10⁻³). It is notable as one of the few metric units in routine US technical/engineering use, since precision manufacturing and electronics are often specified in millimeters even in the US.
Historical origin. Millimeter 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.
Millimeter — sources
- BIPM SI Brochure — SI prefixes — Defines 'milli-' as the prefix for 10⁻³.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many millimeters are in 1 astronomical unit?
1 astronomical unit equals 1.495979e+14 millimeters, using the exact defined conversion factor rather than an estimate.
How do I convert astronomical unit to millimeter?
Multiply the astronomical unit value by 1.495979e+14. The converter above does this instantly to whatever precision you set.
How do I convert millimeter back to astronomical unit?
Use the reverse factor: 1 millimeter equals 6.684587e-15 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 millimeter?
Millimeter (mm) measures distance. A millimeter is one-thousandth of a meter. It is classified as a SI derived (metric prefix) unit.
Is the astronomical unit to millimeter 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.