Light-years to Kilometres Converter

About this calculator

A light-year is a unit of distance, not time: the distance light travels through a vacuum in one Julian year, equal to exactly 9,460,730,472,580.8 km (roughly 9.461 × 10¹² km), based on the defined speed of light (299,792,458 m/s) and a 365.25-day year. Because interstellar distances are unmanageably large in kilometres, astronomers use the light-year (or the closely related parsec) as a more intuitive scale — for example, the nearest star system, Alpha Centauri, is about 4.24 light-years away.

Astronomers, planetarium educators, and science communicators convert light-years to kilometres when a lay audience needs the raw distance made concrete, since "4.24 light-years" is a meaningful comparison to other stars but the roughly 40 trillion km behind it is what conveys the actual scale.