Light-Year Converter

Convert between light-years, parsecs, AU, kilometers, miles, and light-seconds. Includes famous cosmic distances and travel time at light speed.

Light-years
—
Parsecs —
Astronomical Units —
Kilometers —
Extended More scenarios, charts & detailed breakdown ▾
Light-years
—
Parsecs —
AU —
Kilometers —
Professional Full parameters & maximum detail ▾
ly

Parsec Scale

Parsecs —
Kiloparsecs —
Megaparsecs —
Gigaparsecs —

Other Units

Light-years —
Astronomical Units —
Kilometers —

How to Use This Calculator

  1. Enter a distance value and select the source unit.
  2. The result shows the converted distance in all major astronomical units.
  3. Use Travel Time tab to see how long light or a spacecraft takes to cross that distance.
  4. Professional tier shows kiloparsec, megaparsec, gigaparsec, and famous reference distances.

Formula

1 ly = 9.4607304725808×10¹⁵ m  |  1 pc = 3.08568×10¹⁶ m = 3.26156 ly

1 AU = 1.495978707×10¹¹ m  |  1 light-second = 2.99792458×10⁸ m

Example

Proxima Centauri: 4.2441 ly = 4.2441 × 9.461×10¹⁵ m = 4.017×10¹⁶ m = 1.3009 pc = 268,520 AU

Frequently Asked Questions

  • A light-year is the distance light travels in one Julian year (365.25 days) in a vacuum: exactly 9.4607304725808×10¹⁵ meters (about 9.461 trillion km or 5.879 trillion miles).
  • 1 parsec = 3.26156 light-years = 3.0857×10¹⁶ m. A parsec is defined as the distance at which 1 AU subtends a parallax angle of 1 arcsecond.
  • Proxima Centauri is approximately 4.2441 light-years (1.3009 parsecs = 268,545 AU) from Earth. Light from it takes about 4.24 years to reach us.
  • The Andromeda Galaxy (M31) is approximately 2.537 million light-years (0.778 Mpc) away. Its light has been traveling toward us for 2.537 million years.
  • A megaparsec (Mpc) = 1 million parsecs = 3.262 million light-years = 3.0857×10²² m. Megaparsecs are used to measure intergalactic distances and the Hubble constant is expressed in km/s/Mpc.

Related Calculators

🔭 Parsec Calculator 🌠 Hubble Law Calculator 🔴 Redshift Calculator 🌍 Orbital Period Calculator
Sources & References (5) ▾
  1. IAU — Astronomical Unit Definition — International Astronomical Union
  2. NIST Physical Constants — Speed of Light — NIST CODATA
  3. NASA Astrophysics Data System — NASA ADS
  4. OpenStax Astronomy — Distances in Astronomy — OpenStax
  5. JPL Solar System Distances — NASA JPL