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Light Years to km Converter

Convert light-years to kilometres and back — the distance light travels in a year, translated into kilometres your brain can almost grasp.

Convert light-years ⇄ km

4.0113e+13 km
4.24 ly = 4.0113e+13 km

Formula: 4.24 ly (ly × 9.4607 × 10¹²) = 4.0113e+13 km

How the light years to km conversion works

A light-year is 9.4607 trillion kilometres — 9,460,700,000,000 km, to be exact-ish: light travels 299,792,458 metres per second, and a Julian year of 365.25 days gives 9.46073 × 1012 km. So km = light-years × 9.4607 × 1012, and back again light-years = km ÷ 9.4607 × 1012. Because the numbers are astronomically large, the calculator shows results in scientific notation.

Start close to home: Proxima Centauri, the nearest star beyond the Sun, is 4.24 light-years away — 4.24 × 9.4607 × 1012 = 4.011 × 1013 km. Our fastest spacecraft, Voyager 1, travels about 17 km every second, yet it would still need roughly 75,000 years to cover that one gap. The light-year exists precisely because kilometres stop being useful at these scales — but converting back to km is what makes the scale hit home.

Climb the ladder: the Milky Way is about 100,000 light-years across (9.46 × 1017 km), the Andromeda galaxy sits 2.5 million light-years away, and the observable universe stretches about 93 billion light-years in diameter. And a light-year is a distance, not a time — saying a star is 4 light-years away means its light left 4 years ago, but the unit itself measures how far that light travelled.

Handy benchmarks: 1 ly = 9.4607 × 1012 km, 4.24 ly (Proxima Centauri) = 4.011 × 1013 km, 100 ly = 9.4607 × 1014 km and 1,000 ly = 9.4607 × 1015 km. For distances inside the solar system, where light-years are absurdly small, use our AU to km converter instead.

light years to km converter questions

How many km are in one light-year?
One light-year is 9.4607 trillion kilometres (9.46073 × 1012 km). It is the distance light travels in one Julian year (365.25 days) at 299,792,458 metres per second.
How far is Proxima Centauri in km?
Proxima Centauri is 4.24 light-years away, which is 4.24 × 9.4607 × 1012 = 4.011 × 1013 km — about 40 trillion kilometres. It is the closest star to the Sun beyond our own solar system.
Is a light-year a measure of time?
No — it is a distance. The name confuses everyone at first. A light-year measures how far light travels in a year, just as a “car-hour” of driving measures a distance. A star 4 light-years away is seen as it was 4 years ago, but the unit is kilometres by another name.
How do I convert km back to light-years?
Divide kilometres by 9.4607 × 1012: light-years = km ÷ 9.4607 × 1012. Switch the direction above — for example, 1.0 × 1014 km is about 10.57 light-years.
Why not just use kilometres for stars?
Because the numbers become unusable: writing Proxima Centauri's distance as 40,113,000,000,000 km invites dropped digits. Astronomers use light-years for interstellar distances and parsecs for professional work; kilometres stay for solar-system distances.

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Sources & official guidance

Approximate astronomical conversion — 1 light-year = 9.46073 × 10¹² km (Julian year). Stellar distances are approximate and revised as measurements improve. See our disclaimer.