Astronomical units to light-years
Type a value in astronomical units to see it in light-years straight away, or type in the second box to convert back.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Type the value in the astronomical units box.
- Read the result in light-years as you type, and pick the precision you need.
- Swap the direction to convert back, or copy the result.
How it is calculated
ly = au × 0.00001581250741
Multiply the value in astronomical units by 0.00001581250741 to get light-years.
Example
To convert 25 au to light-years: 25 × 0.00001581250741 = 0.000395313 ly.
Conversion table
| Astronomical units (au) | Light-years (ly) |
|---|---|
| 1 | 0.0000158125 |
| 2 | 0.000031625 |
| 3 | 0.0000474375 |
| 5 | 0.0000790625 |
| 10 | 0.000158125 |
| 20 | 0.00031625 |
| 25 | 0.000395313 |
| 50 | 0.000790625 |
| 100 | 0.00158125 |
| 250 | 0.00395313 |
| 500 | 0.00790625 |
| 1,000 | 0.0158125 |
About the units
- Astronomical unit
- The astronomical unit is exactly 149597870700 meters (IAU 2012), close to the mean Earth to Sun distance.
- Light-year
- A light-year is the distance light travels in one Julian year of 365.25 days, exactly 9460730472580800 meters.
Limits and caveats
- Results are rounded for display and computed with the browser's floating point precision (about 15 significant digits).
- Both unit factors are exact by their official definitions.
Questions about this tool
How many light-years are in one astronomical unit?
1 au = 0.0000158125 ly exactly.
How do I convert astronomical units to light-years?
Use ly = au × 0.00001581250741. For example, 25 au = 0.000395313 ly.
How many astronomical units are in one light-year?
1 ly = 63,241.1 au.
Are the inch, foot and mile factors exact or rounded?
They are exact by definition. Since the 1959 agreement one inch is exactly 2.54 cm, one foot 0.3048 m and one mile 1609.344 m.
What is the difference between a mile and a nautical mile?
A statute mile is 1609.344 meters and is used on roads. A nautical mile is 1852 meters and is used at sea and in aviation.