Megaparsec to Light-Year Converter

About this calculator

A megaparsec (Mpc) is one million parsecs, and a parsec itself is defined by parallax — the distance at which one astronomical unit subtends an angle of one arcsecond. Because a parsec equals roughly 3.2616 light-years, one megaparsec works out to about 3,261,563.7 light-years. This converter switches between the two units in either direction using that exact factor.

Megaparsecs are the everyday distance unit of extragalactic astronomy and cosmology: the Andromeda Galaxy sits about 0.78 Mpc away, while the observable universe's radius spans thousands of megaparsecs, and quantities like the Hubble constant are conventionally expressed in km/s per Mpc. Astronomers and astrophysics students switch to light-years when communicating distances more intuitively to a general audience, or when comparing a galactic distance to the travel time of the light being observed — since a galaxy's light-years-away figure is literally how far back in time its light was emitted.