✨ Light Year Distance Converter
Convert between light years and other distance units. A light year is the distance light travels in one year: about 5.879 trillion miles or 9.461 trillion kilometers.
Where the light year comes from
It is a distance, not a duration: how far light gets in one Julian year of exactly 365.25 days. Both numbers in that product are defined rather than measured, so the result is exact.
1 light year = 299,792.458 km/s × 365.25 × 86,400 s
= 9,460,730,472,580.8 km = 5,878,630,000,000 miles = 63,241.1 AUWhichever unit you choose, the entry is converted to light years first and the other three follow. Proxima Centauri at 4.2465 light years returns 40,175,000,000,000 km and 268,553 AU. Andromeda at 2.5 million light years pushes the light-year row into exponential form, as everything prints to six significant figures.
Distances worth having in your head
| Object | Light years |
|---|---|
| The Sun | 0.0000158 |
| Proxima Centauri | 4.25 |
| Sirius | 8.60 |
| Betelgeuse | ~550 |
| Centre of the Milky Way | 26,000 |
| Andromeda Galaxy | 2,500,000 |
Because light takes time to arrive, the distance doubles as a look-back time. You see Sirius as it was 8.6 years ago and Andromeda as it was before our own species existed. Professional papers usually quote parsecs instead; one parsec is 3.26156 light years, so divide to convert.
Frequently asked questions
How many kilometres is a light year?
9,460,730,472,580.8 km, or about 9.46 trillion. In miles it is 5.88 trillion.
Is a light year a measure of time?
No, and the name is the reason people ask. It measures distance. The confusion is useful though: whatever number of light years an object sits at is also the number of years its light has been travelling.
How long would a spacecraft take to cross one light year?
Voyager 1 manages about 17 km per second, so a light year would take it roughly 17,600 years. Nothing we have built comes close to a meaningful fraction of light speed.