Light-Year Converter
Convert light-years, parsecs, AU, km and miles, with travel times.
About this tool
Enter a distance and choose its unit, or pick a preset such as the Moon, Proxima Centauri or the Andromeda Galaxy. Every other unit updates, along with how long the trip would take by spacecraft, by car and at light speed.
Measuring the universe
A light-year is the distance light travels in a Julian year: 9.46 trillion km (5.88 trillion miles). Astronomers often prefer the parsec, 3.26 light-years, defined by parallax: the distance at which the radius of Earth's orbit spans one arcsecond. Inside the solar system, the astronomical unit (AU), the mean EarthβSun distance of 149.6 million km, is handier; sunlight takes 8.3 minutes to cross it. Moonlight takes 1.28 seconds to reach us. The nearest star beyond the Sun, Proxima Centauri, is 4.25 light-years (1.30 parsecs) away; the centre of the Milky Way is about 26,000 light-years; the Andromeda Galaxy about 2.5 million. The travel-time list shows how vast that is: Voyager 1, at 17 km/s, would need around 75,000 years to reach Proxima. Honest limits: a light-year is a distance, not a time; star distances carry measurement uncertainty, and for very distant galaxies the expansion of the universe makes 'distance' depend on which definition is used. The orbital period calculator and the unit converter are related.
Frequently asked questions
How far is a light-year in km?
About 9.46 trillion km (9.4607 Γ 10^12 km).
How many light-years are in a parsec?
About 3.26 light-years.
How far is Proxima Centauri?
About 4.25 light-years, or 1.30 parsecs, roughly 40 trillion km.
How long does light take to reach us from the Sun?
About 8 minutes 20 seconds (1 AU is 8.3 light-minutes).
Is my data sent anywhere?
No. Everything is calculated in your browser, and nothing is stored or sent.