Convert astronomical distances. This free light year calculator turns light-years into kilometres, miles, astronomical units and parsecs — and back — and shows the light-travel time for any distance
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Enter a distance in light-years to see it in kilometres, miles, astronomical units and parsecs — and the time light takes to cross it.
Enter a distance in your chosen unit to convert it into light-years (and the equivalent light-travel time).
In light-years
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Enter a distance
Light-years
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Kilometres
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Miles
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Astronomical units
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Parsecs
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Light travel time
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A light-year is the distance light travels in one year — about 9.46 trillion km (5.88 trillion miles). It’s a measure of distance, not time. Light from the Sun takes about 8.3 minutes to reach Earth.
Use this free light year calculator to convert light-years into kilometres, miles, astronomical units and parsecs — or the other way around — and see the light-travel time for any distance.
What this light year calculator does
A light year calculator converts the astronomical distance unit the light-year into everyday and scientific units. A light-year is how far light travels in one year — a measure of distance, not time.
How far is a light-year?
1 light-year = 9,460,730,472,580,800 m
≈ 9.46 trillion km ≈ 5.88 trillion miles
≈ 63,241 AU ≈ 0.3066 parsecs
It comes from the speed of light (about 299,792 km/s) multiplied by the seconds in a year.
Distance reference points
Object
Distance
Sun to Earth
~8.3 light-minutes (1 AU)
Proxima Centauri
~4.25 light-years
Centre of the Milky Way
~26,000 light-years
Andromeda Galaxy
~2.5 million light-years
Light-years vs parsecs
Astronomers often use parsecs: 1 parsec ≈ 3.26 light-years. Both measure distance; parsecs come from parallax measurements, while light-years are more intuitive for the public.
How to use the light year calculator
Choose a direction — from light-years, or to light-years.
Enter the distance (and unit when converting to light-years).
Read every unit and the light-travel time.
Light Year FAQ
How far is a light-year?
About 9.46 trillion kilometres (5.88 trillion miles) — the distance light travels in one year at roughly 299,792 km/s.
Is a light-year a measure of time?
No. Despite the name, it measures distance — how far light goes in a year, not how long something takes.
How many AU are in a light-year?
About 63,241 astronomical units, where 1 AU is the average Earth–Sun distance.
What's the difference between a light-year and a parsec?
Both are distance units. One parsec is about 3.26 light-years; astronomers often prefer parsecs for measurements.
How long does light from the Sun take to reach us?
About 8.3 minutes, which is roughly 8.3 light-minutes — the Sun is about 1 AU away.
Is the light year calculator free?
Yes, this light year calculator is completely free, needs no sign-up, and gives instant results in your browser.
