Light-Year Converter

Convert light-years, astronomical units (AU) & parsecs.

Convert astronomical distances between light-years, astronomical units (AU), parsecs, metres, kilometres and miles, using exact internationally-defined figures. Accepts scientific notation (2.5e6) and comma-grouped values, shows a live result with a full conversion table, and includes a visual cosmic-distance scale plus interesting facts about light-years, AU and parsecs. Runs fully in your browser — nothing is uploaded.

About Light-Year Converter

Light-Year Converter features

How to use Light-Year Converter

  1. Enter a distance

    Type a non-negative distance into the From field — ordinary decimals, comma-grouped values like 1,000,000, or scientific notation like 2.5e6 all work.

  2. Pick the units

    Choose your from and to units — light-year, astronomical unit, parsec, metre, kilometre or mile — using the searchable dropdowns.

  3. Read the result

    The converted value updates instantly, shown to up to 4 decimal places or in scientific notation for very large or very small numbers.

  4. Swap directions

    Click the swap button to reverse the from and to units — the full-precision result carries across instead of the rounded display value.

  5. Scan the full table

    See your distance expressed in every supported unit at once, and copy any value with one tap.

Frequently asked questions

Is a light-year a distance or a time?

A light-year is a distance, not a time — it's how far light travels through vacuum in one year, about 9.46 trillion km (9,460,730,472,580,800 metres). It's easy to mistake for a time unit because the word "year" is in it, but it always measures length.

How many metres are in one light-year?

One light-year equals exactly 9,460,730,472,580,800 metres. This comes from multiplying the exact speed of light (299,792,458 m/s) by the exact length of a Julian year (31,557,600 seconds).

How many kilometres are in one light-year?

One light-year equals about 9,460,730,472,580.8 kilometres — roughly 9.46 trillion km. Enter 1 in the converter above with light-year and kilometre selected to see it live.

How many miles are in one light-year?

One light-year equals about 5,878,625,373,183.6 miles, using the exact definition of the international mile (1,609.344 metres).

How many astronomical units are in one light-year?

One light-year equals about 63,241.08 astronomical units (AU). That's because a light-year is a far larger distance than the Earth-Sun distance the AU is based on.

How many parsecs are in one light-year?

One light-year equals about 0.3066 parsecs. A parsec is the larger of the two units — about 3.26 times longer than a light-year.

How many light-years are in one parsec?

One parsec equals about 3.26 light-years (more precisely, 3.2616 light-years), since 1 parsec is defined as (648,000 ÷ π) astronomical units.

What is a Julian year?

A Julian year is exactly 365.25 days, or exactly 31,557,600 seconds. It's a fixed, standardised year length (rather than a real calendar year, which varies slightly) used specifically so definitions like the light-year have one exact, unchanging value.

What is an astronomical unit?

An astronomical unit (AU) is a fixed distance of exactly 149,597,870,700 metres, based on the average distance between Earth and the Sun. It's mainly used for distances within our own Solar System, like planetary orbits and spacecraft positions.

What is a parsec?

A parsec is the distance at which one astronomical unit would appear to shift by an angle of one arcsecond, as seen from opposite sides of Earth's orbit (a method called parallax). It equals exactly (648,000 ÷ π) astronomical units, or about 3.26 light-years, and is the standard unit for stellar and galactic distances in professional astronomy.

Can I enter scientific notation?

Yes — the distance field accepts scientific notation such as 2.5e6 (meaning 2.5 million), as well as ordinary decimals and comma-grouped values like 1,000,000.

Why does the result use scientific notation?

Astronomical distances can involve extremely large or extremely small numbers once converted (for example, a light-year in metres has 16 digits). When a plain decimal would be unreadably long, the result switches to scientific notation instead, such as 9.4607e15.

Does ten light-years mean ten years of spacecraft travel?

No. A light-year describes distance — how far light travels in a year — not how long any specific object takes to cover that distance. A real spacecraft has mass and can't reach light speed, so actual travel time depends on its speed, propulsion and route, and would be vastly longer than 10 years for a 10-light-year trip.

Does this include the expansion of the Universe?

No. This is a straightforward unit conversion between fixed distance units and does not account for the expansion of the Universe, which affects how "distance" is even defined for extremely remote galaxies. For everyday astronomical distances (nearby stars, the Solar System) that distinction doesn't matter.

Are my distance values uploaded?

No. The calculation runs entirely in your browser — nothing you type is uploaded, placed in a public URL, or stored anywhere.

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