Light Year Converter

Convert light years to kilometers, meters, astronomical units, or parsecs. See how many kilometers are in 1 light year, common astronomy conversions, and formulas.

999.6K uses Updated · 2026-06-04 Runs locally · zero upload
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Quick answer: how many kilometers are in 1 light year?

1 light year is about 9.4607 x 10^12 kilometers, or about 9,460,700,000,000 kilometers. A light year is not a year of time in this context; it is an astronomy distance unit used for stars, galaxies, and other deep-space objects.

This Light Year Converter can convert light years to kilometers, meters, astronomical units (AU), and parsecs (pc). It can also convert those units back into light years for astronomy homework, science writing, science fiction worldbuilding, classroom examples, and distance checks.

Common light year conversion table

Light yearsKilometersAstronomical units (AU)Parsecs (pc)
0.1 ly9.4607 x 10^11 km6,324.11 AU0.03066 pc
1 ly9.4607 x 10^12 km63,241.1 AU0.3066 pc
4.2465 ly4.0175 x 10^13 km268,632 AU1.302 pc
10 ly9.4607 x 10^13 km632,411 AU3.066 pc
100 ly9.4607 x 10^14 km6,324,110 AU30.66 pc

The 4.2465 ly row is close to the distance from the Sun to Proxima Centauri, which makes it a useful reference point for understanding interstellar distance.

How to use the Light Year Converter

  1. Enter a value - for example 1, 4.2465, or 1000.
  2. Choose the source unit - light years, kilometers, meters, AU, or parsecs.
  3. Choose the target unit - the result updates immediately.
  4. Check the scale - deep-space distances are huge, so scientific notation is often easier to read than the full number.

Formula and theory

1 light year = 9.4607 x 10^12 kilometers
1 light year = 9.4607 x 10^15 meters
1 light year = 63,241.1 astronomical units
1 light year = 0.3066 parsecs

To convert a light-year value to kilometers:

kilometers = light_years × 9.4607 × 10^12

For example, 2.5 light years:

2.5 × 9.4607 × 10^12 = 2.365175 × 10^13 km

Light years, AU, and parsecs

Light years (ly) are common in public science communication and interstellar distances, such as “a star is 10 light years from Earth.”

Astronomical units (AU) are based on the average Earth-Sun distance and are better for solar-system scale distances, such as planetary orbits.

Parsecs (pc) are widely used in professional astronomy because they relate to parallax measurement. Star catalogs, galaxy distances, and astronomy papers often use pc, kpc, and Mpc.

When to use this Light Year Converter

  • Astronomy study - convert between light years, AU, and parsecs from textbook problems.
  • Science writing - translate light years into kilometer values readers can compare.
  • Science fiction settings - estimate interstellar travel distances and keep units consistent.
  • Classroom examples - check the scale of distance, light speed, and travel time problems.
  • Reference checking - compare values from encyclopedias, papers, or observation data.

All calculations happen locally in your browser, so you can revise distances repeatedly without sending data to a server.

Frequently asked questions about Light Year Converter

How many kilometers are in 1 light year?

1 light year is about 9.4607 x 10^12 kilometers, or about 9.46 trillion kilometers.

Is a light year a unit of time or distance?

A light year is a unit of distance. It is the distance light travels in vacuum in one year.

How many astronomical units are in 1 light year?

1 light year is about 63,241.1 astronomical units (AU).

How many parsecs are in 1 light year?

1 light year is about 0.3066 parsecs. In the other direction, 1 parsec is about 3.2616 light years.

Is my data stored?

No. All calculations happen in your browser; nothing is sent to a server.