Light Year Conversion Calculator - Convert Light Years to Kilometers, Miles, AU
Free light year conversion calculator to convert light years to kilometers, miles, astronomical units, parsecs, and meters. Convert between light years and other distance measurements. Perfect for astronomy, space science, and understanding interstellar distances. 1 light year = 9.461 trillion kilometers = 5.88 trillion miles.
Last updated: January 23, 2026
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Conversion Results
Light Years
Light Years
1 ly
Astronomical Units
Astronomical Units
63,242.878764 au
Parsecs
0.30657809 pc
Earth Radii
1,485,010,202.479987 R⊕
Sun Radii
13,586,753.597381 R☉
Metric Units
Meters
9,461,000,000,000,000 m
Kilometers
9,461,000,000,000 km
Imperial/US Units
Miles
5,878,792,849,757.42 mi
Key Facts:
- • 1 light year ≈ 9.461 × 10¹² km ≈ 5.88 trillion miles
- • 1 light year ≈ 63,241 astronomical units
- • 1 light year ≈ 0.3066 parsecs
- • Light travels at 299,792,458 m/s in vacuum
- • Proxima Centauri is about 4.24 light years away
- • A light year is a unit of distance, not time
Light Year Conversion Calculator Features
Definition
1 ly = 9.461 × 10¹² km
Based on the speed of light: 299,792,458 m/s × seconds in a year
Units supported
Light Years, AU, Parsecs, km, mi
Convert between light years, astronomical units, parsecs, and standard units
Use cases
Star Distances, Galaxy Measurements
Ideal for measuring distances to stars, galaxies, and other interstellar objects
Applications
Research, Education, Space Missions
Convert distances for astronomy research, education, and space mission planning
Speed
Instant calculations
See results in all units immediately as you enter or change values
Learning
Understanding Cosmic Scale
Helps visualize and understand the vast distances in our universe
Quick Example Result
For 1 light year:
Kilometers
9.461 trillion km
Miles
5.88 trillion mi
How Our Light Year Conversion Calculator Works
Our light year conversion calculator uses the speed of light in a vacuum (299,792,458 meters per second) multiplied by the number of seconds in a year to calculate the distance light travels in one year. When you enter a distance value in any unit, the calculator first converts it to meters, then displays the equivalent in light years and all other supported units.
Conversion Formulas
Light Year Definition:1 ly = speed of light × seconds in a year1 ly = 299,792,458 m/s × 31,536,000 s1 ly = 9.461 × 10¹⁵ m ≈ 9.461 trillion kmLight Years to Kilometers:km = ly × 9.461 × 10¹²Light Years to Miles:mi = ly × 5.88 × 10¹²Light Years to Astronomical Units:au = ly × 63,241All conversions are based on the speed of light in vacuum and standard astronomical definitions.
What is a Light Year?
A light year (symbol: ly) is a unit of distance used in astronomy to measure vast interstellar and intergalactic distances. Despite its name containing the word "year," a light year is a unit of distance, not time. It represents the distance that light travels in one year through a vacuum.
Distance, Not Time
A light year measures distance, not time. It's the distance light travels in one year at the speed of 299,792,458 meters per second (approximately 186,282 miles per second).
1 ly = 9.461 × 10¹² km = 5.88 × 10¹² mi
Why Use Light Years?
Light years make it easier to express and understand vast interstellar distances. For example, Proxima Centauri is 4.24 light years away, which is much simpler than saying 40.1 trillion kilometers.
Simplifies astronomical distances
How to Convert Light Years to Kilometers
To convert light years to kilometers, multiply the number of light years by 9.461 × 10¹² (9.461 trillion). This is the exact distance light travels in one year.
Example Calculation
To convert 2 light years to kilometers:
2 ly × 9.461 × 10¹² km/ly = 18.922 × 10¹² km= 18,922,000,000,000 kmHow to Convert Light Years to Miles
To convert light years to miles, multiply the number of light years by approximately 5.88 × 10¹² (5.88 trillion miles). This conversion accounts for the difference between kilometers and miles.
Example Calculation
To convert 1 light year to miles:
1 ly × 5.88 × 10¹² mi/ly = 5.88 × 10¹² mi= 5,878,625,373,184 milesHow to Convert Light Years to Astronomical Units
To convert light years to astronomical units, multiply the number of light years by 63,241. One astronomical unit (au) is the average distance from Earth to the Sun, approximately 149.6 million kilometers.
Example Calculation
To convert 5 light years to astronomical units:
5 ly × 63,241 au/ly = 316,205 auLight Year vs. Astronomical Unit vs. Parsec
These three units serve different purposes in astronomy:
Light Year (ly)
Distance light travels in one year. 1 ly ≈ 9.461 × 10¹² km ≈ 63,241 au. Used for interstellar distances.
Use: Star distances, galaxy measurements
Astronomical Unit (au)
Average Earth-Sun distance. 1 au = 149,597,870,700 m. Used for Solar System distances.
Use: Planet distances, asteroid orbits
Parsec (pc)
Distance at which 1 au subtends 1 arcsecond. 1 pc ≈ 3.26 ly ≈ 206,264.8 au. Used in stellar astronomy.
Use: Stellar distances, parallax measurements
Practical Applications
This calculator is essential for various real-world applications:
Astronomy & Space Science
Convert distances for astronomy research, space mission planning, and understanding stellar distances. Essential for calculating travel times and understanding the scale of the universe.
Education & Learning
Help students understand the scale of the universe. Convert between familiar units (km, miles) and light years to visualize interstellar distances.
Space Mission Planning
Convert distances for planning interstellar missions, calculating travel times, and understanding the scale of cosmic distances. Essential for mission design and navigation.
Research & Publications
Convert measurements for scientific papers, research calculations, and astronomical data analysis. Ensure accurate conversions using standard astronomical definitions.
Sources & References
- International Astronomical Union (IAU) - Units and ConstantsStandard definitions for astronomical units and light years
- National Institute of Standards and Technology (NIST) - Speed of Lightc = 299,792,458 m/s (exact value in vacuum)
- NASA Space Science Data Coordinated Archive - Stellar Distance MeasurementsInterstellar distances and stellar data using light years
Need other conversion tools? Check out our astronomical unit calculator and length converter.
Get Custom Calculator for Your PlatformLight Year Conversion Calculator Examples
Input:
- Distance: 1 light year
Conversion Steps:
- Start with 1 light year
- Convert to meters: 1 × 9.461 × 10¹⁵ = 9,461,000,000,000,000 m
- Convert to kilometers: 9.461 × 10¹⁵ ÷ 1,000 = 9.461 × 10¹² km
- Convert to miles: 9.461 × 10¹² km ÷ 1.609344 = 5.88 × 10¹² mi
- Convert to astronomical units: 1 × 63,241 = 63,241 au
Result: 1 ly = 9.461 trillion km = 5.88 trillion miles = 63,241 au
1 light year equals approximately 9.461 trillion kilometers, 5.88 trillion miles, or 63,241 astronomical units.
Input:
- Distance: 4.24 light years
- Context: Distance to Proxima Centauri (nearest star to Sun)
Conversion Steps:
- Start with 4.24 light years
- Convert to meters: 4.24 × 9.461 × 10¹⁵ = 40.1 × 10¹⁵ m
- Convert to kilometers: 40.1 × 10¹⁵ ÷ 1,000 = 40.1 × 10¹² km
- Convert to miles: 40.1 × 10¹² km ÷ 1.609344 = 24.9 × 10¹² mi
- Convert to astronomical units: 4.24 × 63,241 = 268,142 au
Result: 4.24 ly = 40.1 trillion km
Proxima Centauri is 4.24 light years away, which equals approximately 40.1 trillion kilometers or 24.9 trillion miles.
Sirius Distance
8.6 ly ≈
81.4 trillion km
Vega Distance
25 ly ≈
236.5 trillion km
1 Parsec
1 pc =
3.26 light years
Frequently Asked Questions
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