Light-Year Conversion Calculator — ly to km, AU, pc, Miles
Convert any astronomical distance between light-years, kilometres, miles, astronomical units (AU), and parsecs. Results use scientific notation automatically for very large values.
From unit
Distance expressed as light-years (ly)
- 1
Conversion factor to light-years
11 Light-years = 1 ly - 2
Distance in light-years
1 × 1 = 1
How does this calculator work?
One light-year = 9.461 × 10¹² km = 5.879 × 10¹² miles = 63,241 AU = 0.3066 parsecs. Enter a distance in any of these units and the calculator instantly converts to all others. Conversions are exact to the IAU-defined speed of light and astronomical unit.
Formula
How this is calculated
A light-year is the distance light travels in one Julian year (365.25 days) in a vacuum. Using the exact speed of light c = 299,792,458 m/s, one light-year equals exactly 9,460,730,472,580.8 km. The calculator multiplies any input by the appropriate conversion factor derived from this definition.
The other units are defined as follows: one astronomical unit (AU) is the mean Earth–Sun distance, defined as exactly 149,597,870.7 km by the IAU in 2012; one parsec is the distance at which 1 AU subtends an angle of 1 arcsecond, equal to about 3.2616 light-years or 30.857 × 10¹² km. So 1 light-year = 1 / 3.2616 ≈ 0.3066 parsecs, and 1 light-year = 9.461 × 10¹² km / 149,597,870.7 km/AU ≈ 63,241 AU.
These constants are exact by modern IAU definition, so the conversions are exact to the precision shown. Practical astronomers often prefer parsecs (extragalactic scale) or AU (within the Solar System); light-years are common in popular science because "the light from that star left 100 years ago" is intuitively meaningful.
Frequently asked questions
One light-year equals exactly 9,460,730,472,580.8 km — roughly 9.461 × 10¹² km or about 9.5 trillion kilometres. This is the distance light, travelling at 299,792,458 m/s, covers in one Julian year (365.25 days).
A parsec (pc) is a distance unit based on parallax, defined as the distance at which 1 AU subtends an angle of 1 arcsecond. One parsec ≈ 3.2616 light-years ≈ 30.857 × 10¹² km. Professional astronomers prefer parsecs for calculations; light-years are more common in popular science because they convey travel time for light.
Proxima Centauri, the nearest star to the Sun, is about 4.247 light-years (1.302 parsecs or roughly 268,500 AU) from Earth. Its light takes just over four years to reach us — emphasising that even "nearby" cosmic distances are vast by any human standard.
Also known as
TG we-Calculate Editorial Team. (2026). Light-Year Conversion Calculator — ly to km, AU, pc, Miles [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/light-year-conversion-calculator
TG we-Calculate Editorial Team. "Light-Year Conversion Calculator — ly to km, AU, pc, Miles." TG we-Calculate. 2026. https://we-calculate.com/calculator/light-year-conversion-calculator.
TG we-Calculate Editorial Team, "Light-Year Conversion Calculator — ly to km, AU, pc, Miles," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/light-year-conversion-calculator
@misc{wecalculate_light_year_conversion_calculator, title = {Light-Year Conversion Calculator — ly to km, AU, pc, Miles}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/light-year-conversion-calculator}}, year = {2026}, note = {TG we-Calculate} }
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