Light Year Distance Calculator

The Light Year Distance Calculator converts between light years, kilometres, miles, astronomical units (AU), parsecs, light minutes, light seconds and metres — the full range of units used in astronomy to express cosmic distances. A light year is the distance light travels in one vacuum year, approximately 9.461 trillion kilometres (5.879 trillion miles) or 63,241 astronomical units. It is not a unit of time despite containing the word "year".

Astronomical distances are so vast that everyday units become meaningless. The nearest star to our Sun, Proxima Centauri, is 4.243 light years — 40.1 trillion kilometres — away. Light from Proxima Centauri takes 4.243 years to reach Earth, meaning we always see it as it was over 4 years ago. The Andromeda Galaxy is approximately 2.537 million light years distant — so far that its light left before modern humans existed. The observable universe spans about 93 billion light years in diameter, a distance so incomprehensible that even at the speed of light it would take 93 billion years to traverse.

Parsecs (3.2616 light years) are the preferred unit among professional astronomers because they arise naturally from parallax measurements. One AU (the Earth-Sun distance, 149.6 million kilometres) is used within the solar system. Light minutes and light seconds are used for close solar system distances: the Sun is 8.317 light minutes from Earth; the Moon is 1.28 light seconds away. Combine with our Unit Converter for physical measurement conversions and our Scientific Calculator for astronomical calculations in scientific notation. Free, no registration required.