How many kilometers is one light year?

One light year equals exactly 9,460,730,472,580.8 kilometers (roughly 9.461 trillion km). This is the distance light travels in one Julian year (365.25 days) through a vacuum.

How many light years is one kilometer?

One kilometer equals approximately 1.057 × 10^-13 light years, which is an extremely small fraction of a light year. Light covers that distance in about 3.336 microseconds.

What is a light year?

A light year is a unit of distance, not time. It is the distance light travels in one year in a vacuum, approximately 9.461 trillion kilometers or about 5.879 trillion miles.

Why use light years instead of kilometers for space distances?

Stellar and galactic distances expressed in kilometers involve numbers with 15 or more digits, which are difficult to work with. Light years provide a much more manageable scale — for example, the nearest star Proxima Centauri is about 4.24 light years away.

Is this converter accurate?

Yes. The conversion uses the IAU-defined value of 1 light year = 9,460,730,472,580.8 km, which is the internationally accepted standard based on the speed of light and the Julian year.

Kilometers to Light Years Converter

Convert any distance between kilometers and light years in both directions, with full scientific notation and plain number output.

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Light Years (ly)

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Quick Reference Table

Light Years (ly)	Kilometers (km)	Example
0.000016	150,000,000	Earth to Sun (approx.)
0.0063	59,657,519,000	Inner edge of Oort Cloud
1	9,460,730,472,580.8	One light year
4.24	40,113,496,603,262	Proxima Centauri
8.6	81,362,282,063,994	Sirius (brightest star)
26,000	2.46 × 10¹⁷	Center of Milky Way

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Summary

Convert any distance between kilometers and light years in both directions, with full scientific notation and plain number output.

How it works

Enter a distance value in the kilometers field to convert to light years.
Or enter a value in the light years field to convert back to kilometers.
Results appear instantly in both plain and scientific notation.
Use the Swap button to quickly reverse the conversion direction.
Click Copy next to any result to copy the value to your clipboard.

Use cases

Understand how far away stars and galaxies are in everyday units.
Convert astronomical distances for science homework or research.
Check spacecraft travel estimates in relatable km vs. cosmic ly scale.
Compare interstellar distances described in light years to kilometers.
Educational demonstrations of the immense scale of the universe.
Verify figures cited in astronomy articles or textbooks.

Frequently Asked Questions

Last updated: 2026-09-14 · Reviewed by Nham Vu