๐ซLight-Year Converter
Convert light-years to kilometers, miles, AU, and parsecs instantly โ or find out how long light takes to travel any distance.
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Free Light Year Converter
Trying to make sense of cosmic distances? Our free light year converter turns light-years into kilometers, miles, astronomical units (AU), and parsecs in an instant โ and back again. Type a value into any field and watch every other unit update automatically, so you can compare the scale of a nearby star to the width of the Solar System without doing the math yourself.
Beyond simple conversion, the tool includes a light-travel-time mode: enter any distance and see exactly how long light takes to cross it, down to the minute or second for closer objects like the Moon or Sun, and in years for distant stars and galaxies.
Built for students, astronomy enthusiasts, and anyone curious about the universe's true scale. No sign-up, no downloads, no limits โ just accurate conversions whenever you need them. See the About page for the exact constants used, or the FAQ for common questions.
About the Light-Year Converter
Features
Multi-unit conversion table
Enter a value in any unit and see it converted to all others simultaneously.
Light-travel-time mode
Enter a distance and get the time light takes to cross it, formatted in years, days, hours, minutes, or seconds.
Exact physical constants
Uses the defined speed of light (299,792,458 m/s), the IAU-defined AU, and the standard parsec definition.
Scientific notation display
Very large or very small results are shown in both plain decimal and scientific notation.
The constants used
1 light-year = 9,460,730,472,580.8 km (based on the Julian year of 365.25 days and the speed of light 299,792,458 m/s). 1 AU = 149,597,870.7 km. 1 parsec = 3.0856775814913673 ร 10ยนยณ km โ 3.26156 light-years.
Frequently Asked Questions
What is a light-year?
The distance light travels in one Julian year (365.25 days) at 299,792,458 m/s โ about 9.46 trillion kilometers.
How does this converter work?
Enter a value in any supported unit (light-years, AU, parsecs, km, miles, etc.) and every other unit updates instantly.
Is it free?
Completely free, no sign-up, downloads, or limits.
What units can I convert between?
Light-years, light-seconds/minutes/hours/days, astronomical units, parsecs, kilometers, and miles.
What's the difference between a light-year and a parsec?
A parsec is about 3.26 light-years; both measure astronomical distance, but parsecs are derived from stellar parallax angles.
Can I find out how long light takes to travel a distance?
Yes, use the light-travel-time mode: enter a distance and get the travel time formatted in years, days, hours, minutes, or seconds.
How accurate are the conversions?
Uses the exact defined speed of light and standard AU/parsec definitions for precise results.
Does it handle very large or small numbers?
Yes, results are shown in both scientific notation and plain decimal.
Is my data stored?
No; everything runs in your browser and isn't stored or sent anywhere.
Does it work on mobile?
Yes, fully responsive on all screen sizes.