Convert Astronomical Unit to Sun's Radius
Convert astronomical units to sun's radii instantly. 1 astronomical unit = 215.0321556705 sun's radius — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Sun's Radius 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.
Sun's Radius
The Sun's radius is approximately 695,700 km (6.957×10⁸ m), defined as the IAU 2015 nominal solar radius for use in stellar physics and exoplanet research.
The IAU (International Astronomical Union) Resolution B3 in 2015 defined a nominal solar radius of exactly 6.957×10⁸ m to serve as a stable reference, independent of actual measurement-uncertainty variations in the real Sun.
Solar radii are used in stellar physics, exoplanet characterisation, and any context where a star's size is expressed relative to the Sun. Most stellar radius measurements are quoted in solar-radius units rather than meters.
Defined exactly at 6.957×10⁸ m by IAU Resolution B3 in 2015.
Astronomical Unit to Sun's Radius conversion formula
The relationship between astronomical units and sun's radii:
To convert astronomical units to sun's radii, multiply the value in astronomical units by 215.0321556705. To reverse, multiply sun's radii by 0.0046504673.
How to use this converter
Type a value into the calculator. The result in sun's radii updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Sun's Radius to Astronomical Unit converter for the reverse direction.
Step-by-step: convert astronomical units to sun's radii
- Write down the value in astronomical units (AU).
- Multiply that value by the factor 215.0321556705.
- The product is the equivalent value in sun's radii (R☉).
- To reverse, multiply the sun's radius value by 0.0046504673.
Worked examples
Example 1 — Convert 1 AU to R☉:
1 × 215.0321556705 = 215.0321556705 R☉
Example 2 — Convert 100 AU to R☉:
100 × 215.0321556705 = 21503.2155670548 R☉
Astronomical Unit to Sun's Radius conversion table
Standard reference values for converting astronomical units to sun's radii:
| Astronomical Unit [AU] | Sun's Radius [R☉] |
|---|---|
| 0.01 | 2.1503215567 |
| 0.1 | 21.5032155671 |
| 1 | 215.0321556705 |
| 2 | 430.0643113411 |
| 3 | 645.0964670116 |
| 4 | 860.1286226822 |
| 5 | 1075.1607783527 |
| 10 | 2150.3215567055 |
| 20 | 4300.643113411 |
| 30 | 6450.9646701164 |
| 40 | 8601.2862268219 |
| 50 | 10751.6077835274 |
| 100 | 21503.2155670548 |
| 500 | 107516.0778352738 |
| 1000 | 215032.1556705476 |
Frequently asked questions
How many sun's radii is 1 astronomical unit?
How do I convert astronomical units to sun's radii?
How do I convert sun's radii back to astronomical units?
How many sun's radii is 100 astronomical units?
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Sources & references
Conversion factor (1 AU = 215.0321556705 R☉) 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.