Light Years to Kilometers Converter
Convert light years to kilometers instantly. Enter light-years to get km using the 9.46 trillion km factor, with the reverse km to light-years direction.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the Light Years to Kilometers Converter Works
This tool converts light-years (ly) to kilometers (km) and back. A light-year is the distance light travels in one year, used in astronomy because the gaps between stars are far too large to express comfortably in kilometers.
The Formula
Kilometers = light-years × 9,460,730,472,580.8 Light-years = kilometers ÷ 9,460,730,472,580.8
The factor comes from the speed of light (299,792,458 m/s) multiplied by the number of seconds in a Julian year (365.25 days).
Worked Example
Convert 1 light-year to kilometers:
- km = 1 × 9,460,730,472,580.8 = about 9.46 × 10^12 km
The distance to Proxima Centauri, about 4.25 light-years:
- km = 4.25 × 9.46 × 10^12 = about 4.0 × 10^13 km
Going the other way, 1 trillion km in light-years:
- ly = 1 × 10^12 ÷ 9.46 × 10^12 = about 0.106 light-years
Light Years to Kilometers Quick Reference
| Light-years | Kilometers (approx.) |
|---|---|
| 1 | 9.46 × 10^12 |
| 4.25 | 4.02 × 10^13 |
| 10 | 9.46 × 10^13 |
| 100 | 9.46 × 10^14 |
| 1000 | 9.46 × 10^15 |
Why Astronomers Use Light-Years
Kilometers become unwieldy at cosmic scales: the nearest star is tens of trillions of kilometers away. The light-year packages that distance into a single, intuitive unit tied to the speed of light. It also reminds us that we see distant objects as they were in the past, since their light took years to reach us.
Frequently asked questions
How many kilometers are in a light year?+
One light-year equals about 9.46 trillion kilometers, exactly 9,460,730,472,580.8 km. This is the distance light travels in one year through a vacuum.
How do I convert light years to kilometers?+
Multiply the number of light-years by 9,460,730,472,580.8. For example, 1 light-year is about 9.46 × 10^12 km. To reverse it, divide kilometers by the same factor.
How far is the nearest star in kilometers?+
Proxima Centauri is about 4.25 light-years away, which is roughly 4.0 × 10^13 km, or about 40 trillion kilometers. Even the closest star is an enormous distance in kilometers.
How is a light year defined?+
A light-year is the distance light travels in one Julian year (365.25 days) in a vacuum, at 299,792,458 meters per second. Multiplying speed by time gives 9.46 trillion kilometers.
Is a light year a unit of time or distance?+
Distance, not time. Despite the word year, a light-year measures how far light travels in a year, making it a convenient unit for the vast distances between stars.