Astronomical distance converter
Type a distance, choose the units, and see the result in every common unit. The factors come from the IAU definitions of the astronomical unit, the light-year and the parsec.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Type a number. A dot or a comma works as the decimal separator; scientific notation such as 1e6 is understood.
- Choose the unit you have and the unit you need. The ⇄ button swaps them.
- The table shows the same distance in all common units at once.
Definitions
Every unit is converted through the metre.
| Unit |
In metres |
| 1 astronomical unit |
149,597,870,700 (exact) |
| 1 light-second |
299,792,458 (exact) |
| 1 light-year |
9,460,730,472,580,800 (exact) |
| 1 parsec |
648,000/π au ≈ 3.0856776 × 10¹⁶ |
The light-year uses the Julian year of 365.25 days (31,557,600 s).
Worked example
Proxima Centauri is about 4.24 light-years away: 4.24 ÷ 3.26156 = 1.30 parsecs, or 4.24 × 63,241 = 268,000 au. The mean Earth–Sun distance of 1 au is 149.6 million km.
Tips
- Parallax distances are given in parsecs; popular articles use light-years.
- Results over about 10¹⁵ are shown in scientific notation.
Frequently asked questions
How many kilometres are in an astronomical unit?
Exactly 149,597,870.7 km. Since 2012 the au is defined as 149,597,870,700 metres.
How long is a light-year?
9,460,730,472,580,800 m, or about 9.46 trillion km. It is the distance light travels in a vacuum in one Julian year of 365.25 days, at 299,792,458 m/s.
How many light-years is a parsec?
About 3.26156 light-years. A parsec is 648,000/π astronomical units, about 206,264.8 au or 3.0857 × 10¹⁶ m.
How long does light take to travel from the Sun to Earth?
One au is about 8.3167 light-minutes, so sunlight takes a little over 8 minutes to reach Earth on average.