Convert Astronomical Unit to A.u. of Length
Convert astronomical units to a.u. of length instantly. 1 astronomical unit = 2.82699e+21 a.u. of length — use the live calculator, the exact formula, a conversion table and worked examples. Also check the A.u. of Length to Astronomical Unit converter for the reverse conversion.
Units explained
Astronomical Unit
The astronomical unit (AU) is a unit of length equal to exactly 149,597,870,700 meters, approximately the average distance from Earth to the Sun. It is the fundamental unit for distance within the solar system.
The AU was originally defined as the semi-major axis of Earth's orbit. In 2012, IAU Resolution B2 redefined the AU as exactly 149,597,870,700 meters, severing its dependence on the actual fluctuating Earth–Sun distance.
AUs are used to express distances within the solar system (Mars: 1.5 AU, Pluto: ~40 AU at perihelion), exoplanet orbital radii, and other planetary-scale distances. Standard in planetary science and astronomy.
Original definition tied to Earth's orbit (Newton, 17th century); fixed at exactly 149,597,870,700 m by IAU Resolution B2 in 2012.
A.u. of Length
The atomic unit of length (a.u.) is equal to the Bohr radius — approximately 5.292×10⁻¹¹ m. Despite the abbreviation matching 'astronomical unit', this is a different unit used in atomic and molecular physics.
The atomic unit system was developed in the 1950s for quantum-chemistry calculations. The a.u. of length is defined as the Bohr radius (a₀), the most probable distance between the proton and electron in a hydrogen atom in its ground state.
The atomic unit of length is used throughout quantum chemistry, electronic-structure theory, and computational physics. Most quantum-mechanical equations simplify when expressed in atomic units rather than SI units.
Atomic unit system developed by Hartree in the 1920s; value fixed via CODATA 2018 determination of fundamental physical constants.
Astronomical Unit to A.u. of Length conversion formula
The relationship between astronomical units and a.u. of length:
To convert astronomical units to a.u. of length, multiply the value in astronomical units by 2.82699e+21. To reverse, multiply a.u. of length by 3.537331e-22.
How to use this converter
Type a value into the calculator. The result in a.u. of length updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the A.u. of Length to Astronomical Unit converter for the reverse direction.
Step-by-step: convert astronomical units to a.u. of length
- Write down the value in astronomical units (AU).
- Multiply that value by the factor 2.82699e+21.
- The product is the equivalent value in a.u. of length (a.u.).
- To reverse, multiply the a.u. of length value by 3.537331e-22.
Worked examples
Example 1 — Convert 1 AU to a.u.:
1 × 2.82699e+21 = 2.82699e+21 a.u.
Example 2 — Convert 100 AU to a.u.:
100 × 2.82699e+21 = 2.82699e+23 a.u.
Astronomical Unit to A.u. of Length conversion table
Standard reference values for converting astronomical units to a.u. of length:
| Astronomical Unit [AU] | A.u. of Length [a.u.] |
|---|---|
| 0.01 | 2.82699e+19 |
| 0.1 | 2.82699e+20 |
| 1 | 2.82699e+21 |
| 2 | 5.65398e+21 |
| 3 | 8.48097e+21 |
| 4 | 1.130796e+22 |
| 5 | 1.413495e+22 |
| 10 | 2.82699e+22 |
| 20 | 5.65398e+22 |
| 30 | 8.48097e+22 |
| 40 | 1.130796e+23 |
| 50 | 1.413495e+23 |
| 100 | 2.82699e+23 |
| 500 | 1.413495e+24 |
| 1000 | 2.82699e+24 |
Frequently asked questions
How many a.u. of length is 1 astronomical unit?
How do I convert astronomical units to a.u. of length?
How do I convert a.u. of length back to astronomical units?
How many a.u. of length is 100 astronomical units?
Popular length unit conversions
Convert Astronomical Unit to other length units
Show all Astronomical Unit conversions
Metric / SI (4 units)
Imperial / US Customary (4 units)
Astronomical (8 units)
Sources & references
Conversion factor (1 AU = 2.82699e+21 a.u.) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.