ConverterHub

Parsec to Light-Year Converter

Enter a distance in parsecs to convert it to light-years and more.

How it is calculated

The tool multiplies the distance in parsecs by three constants: ly = pc × 3.2615637769, AU = pc × 206264.806 and km = pc × 3.0856775815×10¹³. Light-years are shown with four decimals, astronomical units with two decimals, and kilometres in scientific notation such as 4.0114e+13, meaning 4.0114 × 10¹³. Any number is accepted, including very small or very large values; for distances in kiloparsecs or megaparsecs, multiply by 1,000 or 1,000,000 before entering. The light-year here is the distance light travels in one Julian year in vacuum. Remember that the result is only as precise as the parsec distance you start with.

Worked example

A star is measured at 1.3 parsecs. Light-years: 1.3 × 3.2615637769 = 4.23999, shown as 4.2400 ly. Astronomical units: 1.3 × 206,264.806 = 268,144.25 AU. Kilometres: 1.3 × 3.0856775815×10¹³ = 4.0114e+13 km, about 40 trillion kilometres. Light from the star therefore needs a little over four years to reach us.

Try this example →

Common mistakes

  • Treating the parsec as a unit of time like the light-year; both are distances, and a parsec is about 3.26 times longer.
  • Entering kiloparsecs without multiplying by 1,000 first, which makes the result 1,000 times too small.
  • Reading 4.0114e+13 as 4.0114 or as 40,114; the e+13 part means multiply by 10 to the power 13.
  • Rounding 3.26 or 3.3 for catalog distances, where the extra digits matter for nearby stars.

About this calculator

A parsec (parallax-second) is the distance at which one astronomical unit — the Earth-Sun distance — subtends an angle of exactly one arcsecond, defined geometrically rather than by light travel time. It works out to about 3.2616 light-years, 206,265 astronomical units, or 3.0857×10¹³ kilometers, and it's the unit astronomers get directly from parallax measurements rather than deriving.

This converter takes a distance in parsecs and returns the equivalent in light-years, astronomical units, and kilometers using the exact IAU-defined constants, so you don't have to remember the conversion factors or risk rounding errors. Astronomy students, amateur stargazers, and science writers use it to translate catalog distances — which are usually given in parsecs or kiloparsecs from parallax or standard-candle measurements — into the light-year figures that are more intuitive for a general audience.

Was this helpful?

You can pick up to 3 reactions.

Comments (0)

  • Be the first to comment.

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators