Equivalent distance
Your value in light years, parsecs, and astronomical units.
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Astronomical
Light Year Conversion
Convert light years to kilometers, miles, astronomical units, and parsecs instantly, with a full equivalents table and comparison chart.
Result
9.46 trillion km
How it works
A light year is the distance light travels in one year through a vacuum, about 9.46 trillion kilometers. Astronomers also use the parsec, which is a bit larger. All these units scale from the meter.
1 light year ≈ 9.4607 × 10¹² km
1 parsec ≈ 3.2616 light years ≈ 206,265 AU
1 parsec ≈ 3.2616 light years ≈ 206,265 AU
Worked example
Proxima Centauri is about 4.24 light years away, which is roughly 4.24 × 9.46 = 40.1 trillion km.
How far is a light-year? Examples
A light-year is the distance light travels in a Julian year of 365.25 days: 9,460,730,472,580.8 km, about 5.88 trillion miles or 63,241 AU. Astronomers also use the parsec, which is about 3.2616 light-years.
| Object | Distance |
|---|---|
| Proxima Centauri (nearest star) | 4.24 ly = 40.1 trillion km |
| Sirius | 8.6 ly |
| Center of the Milky Way | about 26,000 ly |
| Andromeda Galaxy | about 2.5 million ly |
| 1 parsec | 3.2616 ly = 30.9 trillion km |
Because light takes years to arrive, a star's distance in light-years also tells you how old the light you see is: the light from Sirius left it about eight and a half years ago.
Light-year conversion factors
| 1 light-year equals | Value |
|---|---|
| Kilometers | 9,460,730,472,580.8 km |
| Miles | about 5.879 trillion mi |
| Astronomical units | about 63,241 AU |
| Parsecs | about 0.3066 pc |
| Light travel time | 1 Julian year (365.25 days) |
Light-years, parsecs and AU: which to use
| Unit | Size | Best for |
|---|---|---|
| Astronomical unit (AU) | 149.6 million km | Planets, asteroids and comets |
| Light-year (ly) | 9.46 trillion km | Star and galaxy distances in news and education |
| Parsec (pc) | 3.26 ly | Research papers; measured directly from parallax |
| Kiloparsec / megaparsec | 1,000 pc / 1,000,000 pc | Galaxy structure and the distances between galaxies |
More distances in light-years
| Object | Distance |
|---|---|
| Alpha Centauri A and B | 4.37 ly |
| Polaris (North Star) | about 430 ly |
| Betelgeuse | roughly 550 to 700 ly |
| Orion Nebula | about 1,340 ly |
| Large Magellanic Cloud | about 160,000 ly |
| Edge of the observable universe | about 46.5 billion ly (radius) |
How long would a light-year take to travel?
- At Voyager 1's speed (about 17 km/s), one light-year takes roughly 17,600 years.
- At the Parker Solar Probe's record speed (about 190 km/s), roughly 1,600 years.
- A passenger jet at 900 km/h would need about 1.2 million years.
A common mix-up
Despite the name, a light-year measures distance, not time. Saying a star is "10 light-years away" means its light has traveled for 10 years to reach us. To convert distances to travel times, use the light travel time calculator; for solar system distances, the AU calculator gives tidier numbers.
Frequently asked questions
How many kilometers are in a light-year?
About 9.461 trillion km (9.4607 × 10¹² km), or 5.879 trillion miles.
How many light-years is a parsec?
About 3.2616 light-years.
How long would it take to travel one light-year?
At the speed of the fastest spacecraft so far (Parker Solar Probe, about 190 km/s), roughly 1,600 years.
How many miles is a light-year?
About 5.88 trillion miles (5,878,625,373,184 mi).
Is a light-year time or distance?
Distance. It is how far light travels in one Julian year of 365.25 days.
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