Convert Parsec to Light Year
Convert parsecs to light years instantly. 1 parsec = 3.2615637772 light year — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Light Year to Parsec converter for the reverse conversion.
Units explained
Parsec
A parsec (parallax-second) is a distance unit equal to 648,000/π astronomical units — approximately 3.086×10¹⁶ m (3.26 light years). It is the standard distance unit in professional astronomy.
Defined as the distance at which one astronomical unit subtends an angle of one arcsecond. IAU Resolution B2 in 2015 made this an exact definition: 1 pc = (648,000/π) AU.
Parsecs are used in professional astronomy for stellar distances (Proxima Centauri ≈ 1.3 pc), galactic-scale distances (with prefixes kiloparsec and megaparsec), and parallax measurements. Standard since the early 20th century.
Concept introduced by Herbert Hall Turner in 1913; exact definition via the AU adopted by IAU Resolution B2 in 2015.
Light Year
A light year is the distance light travels in one Julian year in vacuum — exactly 9,460,730,472,580,800 meters (about 9.46×10¹⁵ m). It is the most common unit for expressing inter-stellar distances in non-technical astronomy.
Defined as the speed of light (299,792,458 m/s, exact) multiplied by one Julian year (365.25 days × 86400 seconds/day). Both factors are exact, making the light year exact by definition.
Light years are used in popular astronomy, science journalism, and stellar distance descriptions. The nearest star (Proxima Centauri) is 4.24 ly away; the Milky Way is about 100,000 ly across.
Concept of distance-as-time used since the 19th century; the modern exact definition follows from the 1983 SI definition of the meter via the speed of light.
Parsec to Light Year conversion formula
The relationship between parsecs and light years:
To convert parsecs to light years, multiply the value in parsecs by 3.2615637772. To reverse, multiply light years by 0.3066013938.
How to use this converter
Type a value into the calculator. The result in light years updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Light Year to Parsec converter for the reverse direction.
Step-by-step: convert parsecs to light years
- Write down the value in parsecs (pc).
- Multiply that value by the factor 3.2615637772.
- The product is the equivalent value in light years (ly).
- To reverse, multiply the light year value by 0.3066013938.
Worked examples
Example 1 — Convert 1 pc to ly:
1 × 3.2615637772 = 3.2615637772 ly
Example 2 — Convert 100 pc to ly:
100 × 3.2615637772 = 326.1563777167 ly
Parsec to Light Year conversion table
Standard reference values for converting parsecs to light years:
| Parsec [pc] | Light Year [ly] |
|---|---|
| 0.01 | 0.0326156378 |
| 0.1 | 0.3261563777 |
| 1 | 3.2615637772 |
| 2 | 6.5231275543 |
| 3 | 9.7846913315 |
| 4 | 13.0462551087 |
| 5 | 16.3078188858 |
| 10 | 32.6156377717 |
| 20 | 65.2312755433 |
| 30 | 97.846913315 |
| 40 | 130.4625510867 |
| 50 | 163.0781888584 |
| 100 | 326.1563777167 |
| 500 | 1630.7818885837 |
| 1000 | 3261.5637771674 |
Frequently asked questions
How many light years is 1 parsec?
How do I convert parsecs to light years?
How do I convert light years back to parsecs?
How many light years is 100 parsecs?
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Sources & references
Conversion factor (1 pc = 3.2615637772 ly) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.