About the Light-Year Converter
A free tool for converting between astronomical distance units and calculating light travel time.
What it is
The Light-Year Converter converts a distance between light-years, light-seconds/minutes/hours/days, astronomical units (AU), parsecs, kilometers, and miles — all at once, updating live as you type. A second mode calculates how long light takes to travel any given distance.
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 × 10¹³ km ≈ 3.26156 light-years.