Light-Years to Kilometers Converter (ly to km)
1 ly = 9,460,730,472,580.8 km exactly. Convert light-years to kilometers for star and galaxy distances, with ly to km and km to ly charts.
Kilometer (km) = Light Year (ly) × 9460730472580
Light Year (ly): A light-year is the distance light travels in a vacuum in one Julian year of 365.25 days. Using 86,400 seconds per day and c = 299,792,458 m/s gives exactly 9,460,730,472,580,800 metres.
Kilometer (km): The kilometre is 1,000 metres. One international mile is exactly 1.609344 km; to convert kilometres to miles, divide by 1.609344.
| Light Year (ly) | Kilometer (km) |
|---|---|
| 1 | 9460730472580 |
| 5 | 47303652362900 |
| 10 | 94607304725800 |
| 25 | 236518261815000 |
| 50 | 473036523629000 |
| 100 | 946073047258000 |
A light-year is a distance, not a length of time: it is how far light travels in a vacuum in one Julian year of 365.25 days. With the speed of light fixed at exactly 299,792,458 m/s, that comes to exactly 9,460,730,472,580.8 km, about 9.46 trillion kilometers. Astronomers use it because star distances written in kilometers run to 13 digits and more.
Converting the other way shows how fast the numbers grow. Proxima Centauri, the nearest star beyond the Sun, lies about 4.25 light-years away, roughly 40 trillion km, and the Andromeda Galaxy about 2.5 million light-years away. Professional catalogs often use the parsec instead, about 3.26 light-years; the length converter includes it along with the astronomical unit.
How to use this tool
- Type a value in the Light Year box to see it in kilometers, or type in the Kilometer box to convert the other way.
- Press ⇄ to swap the two units, or Load example for a typical value.
- Check the charts below for common values; for other units, open the Length converter.
Formula
Kilometer (km) = Light Year (ly) × 9460730472580
Light Year (ly) = Kilometer (km) × 1.05700083402e-13
Both factors come from exact definitions: 1 kilometer = 1.05700083402e-13 light years and 1 light year = 9460730472580 kilometers (shown to 12 significant digits).
Example
Two conversions worked with the same factors the converter uses:
4.25 ly × 9460730472580 ≈ 40208100000000 km
100000000000000 km × 1.05700083402e-13 ≈ 10.57 ly
Light Year to Kilometer chart
Common values from light years to kilometers, rounded to four decimal places.
| Light Year (ly) | Kilometer (km) |
|---|---|
| 0.001 | 9,460,730,473 |
| 0.01 | 94,607,304,730 |
| 0.1 | 946,073,047,300 |
| 0.5 | 4,730,365,236,000 |
| 1 | 9,460,730,473,000 |
| 2 | 18,921,460,950,000 |
| 3 | 28,382,191,420,000 |
| 4.25 | 40,208,104,510,000 |
| 5 | 47,303,652,360,000 |
| 8.6 | 81,362,282,060,000 |
| 10 | 94,607,304,730,000 |
| 25 | 236,518,261,800,000 |
| 50 | 473,036,523,600,000 |
| 100 | 946,073,047,300,000 |
| 250 | 2,365,182,618,000,000 |
| 500 | 4,730,365,236,000,000 |
| 1,000 | 9,460,730,473,000,000 |
| 10,000 | 94,607,304,730,000,000 |
| 26,000 | 245,978,992,300,000,000 |
| 100,000 | 946,073,047,300,000,000 |
| 1,000,000 | 9,460,730,473,000,000,000 |
Kilometer to Light Year chart
The reverse direction for values people often look up.
| Kilometer (km) | Light Year (ly) |
|---|---|
| 1,000,000,000,000 | 0.1057 |
| 5,000,000,000,000 | 0.5285 |
| 10,000,000,000,000 | 1.057 |
| 40,000,000,000,000 | 4.228 |
| 100,000,000,000,000 | 10.57 |
| 500,000,000,000,000 | 52.85 |
| 1,000,000,000,000,000 | 105.7001 |
| 10,000,000,000,000,000 | 1,057 |
| 100,000,000,000,000,000 | 10,570.01 |
| 1,000,000,000,000,000,000 | 105,700.08 |
Distances measured in light-years
| Object | Light Year (ly) | Kilometer (km) |
|---|---|---|
| Proxima Centauri, the nearest star to the Sun | 4.25 | 40,208,104,510,000 |
| Sirius, the brightest star in the night sky | 8.6 | 81,362,282,060,000 |
| Vega, a bright star of the northern summer sky, about | 25 | 236,518,261,800,000 |
| One parsec, the professional distance unit | 3.2616 | 30,856,775,810,000 |
| Center of the Milky Way, about | 26,000 | 245,978,992,300,000,000 |
| Large Magellanic Cloud, about | 160,000 | 1,513,716,876,000,000,000 |
| Andromeda Galaxy, about | 2,500,000 | 23,651,826,180,000,000,000 |
Quick mental estimate
Treat a light-year as 9.5 trillion km: 4 ly → 38 trillion km, against an exact 37.84 trillion. That is about 0.4% high; rounding all the way to 10 trillion km per light-year is about 5.7% high, still fine for a sense of scale.
Use the converter or the charts when the exact figure matters.
The two units
Light Year (ly): A light-year is the distance light travels in a vacuum in one Julian year of 365.25 days. Using 86,400 seconds per day and c = 299,792,458 m/s gives exactly 9,460,730,472,580,800 metres.
Kilometer (km): The kilometre is 1,000 metres. One international mile is exactly 1.609344 km; to convert kilometres to miles, divide by 1.609344.
Frequently asked questions
Is a light-year a measure of time?
No, it measures distance; the year only sets how long the light travels. Because of that, looking at a star 100 light-years away shows light that left it about 100 years ago.
How long does sunlight take to reach Earth?
About 8.3 minutes. The astronomical unit, close to the average Earth–Sun distance, is defined as exactly 149,597,870.7 km, only about 0.0000158 of a light-year.
Why does the light-year use a 365.25-day year?
The International Astronomical Union bases it on the Julian year of exactly 365.25 days of 86,400 seconds, which makes the light-year an exact number of meters. A calendar year changes length, so it could not give a fixed distance.
How precise is the result?
The converter uses the exact definitions above with browser floating-point arithmetic and shows up to 12 significant digits. The charts round to four decimal places for reading.
Sources
Last updated:
Page address with these inputs: https://kakao.mobile/tools/light-year-to-kilometer-converter/
Cite or embed this tool
kakaoCalc. (2026, November 8). Light-Years to Kilometers Converter (ly to km). https://kakao.mobile/tools/light-year-to-kilometer-converter/
“Light-Years to Kilometers Converter (ly to km).” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/light-year-to-kilometer-converter/.
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