Light-Year Distance Calculator
Convert between light-years, parsecs, astronomical units, kilometres and miles.
About the Light-Year Distance Calculator
Enter a distance and choose its unit. The calculator converts it to every other unit and gives how long light takes to cross it.
A light-year is the distance light travels in a Julian year (365.25 days): exactly 9,460,730,472,580.8 km. The astronomical unit is exactly 149,597,870,700 m (IAU 2012), and a parsec is 648,000/π AU, about 3.26 light-years.
The formula
1 ly = c × 365.25 × 86,400 s; 1 pc = 648,000 ÷ π AU
Worked example
Proxima Centauri, the nearest star, at 4.2465 light-years
- 4.2465 × 9.4607 × 10¹² km
- = 4.0175 × 10¹³ km, about 40 trillion km
- Its light set out 4.25 years ago
Questions people ask
Is a light-year a time?
No, it's a distance.
Why do astronomers use parsecs?
They come directly from parallax measurements.
How far is the Sun in light terms?
1 AU, about 8 minutes 19 seconds of light travel.