To convert parsecs to light-years, multiply by 3.261563777. That factor is the whole relationship: both units measure length, so the conversion is a proportion with no offset and no substance-specific constant.
The distance at which one astronomical unit subtends one arcsecond: about 3.26 light-years. The distance light covers in one Julian year — about 9.46 trillion kilometres.
The mil and the millimetre are not the same thing and are out by a factor of about forty. A mil is one thousandth of an inch — 0.0254 mm — and a spec sheet that quotes film thickness in mils means the small unit. British drawings write the same size as "thou". The tables underneath give both a plain step-by-step lookup and a list of real quantities expressed in light-years, so you can sanity-check whether your answer is a plausible size.
The formula
parsecs- The amount you are converting, in parsecs
3.26156377717- The exact number of light-years in one parsec
light-years- The converted result
How it works, step by step
- Enter the value in parsecs.
- It is multiplied by 3.26156377717, the exact factor between the two units.
- The answer is shown in light-years, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A larger figure: 100 pc in light-years
Take a larger figure, roughly 100 pc. The conversion is a single multiplication — 100 × 3.26156 — giving 326.156 ly. Because the relationship is proportional, doubling the input doubles the answer to 652.313 ly.
A round figure: 1 pc in light-years
A round figure comes to about 1 pc. Multiplying by the factor: 1 × 3.26156 = 3.26156 ly. Dividing the answer back by 3.26156 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
How to read your score
Frequently asked questions
How many light-years are in one parsec?
Exactly 3.26156377717. Every figure on this page is that one number multiplied by your input, so the only rounding is at the display step.
What is the formula to convert parsecs to light-years?
light-years = parsecs × 3.26156377717. Reversed, parsecs = light-years ÷ 3.26156377717, which is the same as multiplying by 0.306601393786.
Which is the bigger unit, the parsec or the light-year?
The parsec. One parsec equals 3.26156 light-years.
What does this quantity actually measure?
Both units measure length. That is why a single factor is enough: there is no temperature offset and no material property involved, unlike conversions that cross between different quantities.
What is a parsec?
The distance at which one astronomical unit subtends one arcsecond: about 3.26 light-years.
What is a light-year?
The distance light covers in one Julian year — about 9.46 trillion kilometres.
Why does my answer differ from another converter?
Almost always because the other tool rounded the factor before multiplying. This page keeps full double precision through the calculation and rounds only for display, and it prints the factor it used so you can see where any difference came from.
Is there a quick way to do pc to ly in my head?
Plenty of people do this in their head: multiply by 3.3 instead of using the exact factor 3.261563777. At 100 that shortcut gives 330 light-years, off by 3.844 light-years or about 1.18%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Parsecs to light-years reference tables
| Parsecs | Light-Years |
|---|---|
| 0.5 pc | 1.63078 ly |
| 1 pc | 3.26156 ly |
| 2 pc | 6.52313 ly |
| 3 pc | 9.78469 ly |
| 5 pc | 16.3078 ly |
| 10 pc | 32.6156 ly |
| 20 pc | 65.2313 ly |
| 25 pc | 81.5391 ly |
| 50 pc | 163.078 ly |
| 75 pc | 244.617 ly |
| 100 pc | 326.156 ly |
| 250 pc | 815.391 ly |
| 500 pc | 1630.78 ly |
| 1000 pc | 3261.56 ly |
| 5000 pc | 16,307.8 ly |
Exact factor: 1 parsec = 3.26156377717 light-years.
| Quantity | pc | ly |
|---|---|---|
| A credit card’s long edge | 2.774e-18 pc | 9.048e-18 ly |
| A door height | 6.585e-17 pc | 2.148e-16 ly |
| An Olympic pool | 1.620e-15 pc | 5.285e-15 ly |
| The Eiffel Tower | 1.069e-14 pc | 3.488e-14 ly |
| A marathon | 1.367e-12 pc | 4.460e-12 ly |
| Earth’s diameter | 4.129e-10 pc | 1.347e-09 ly |
Published reference values, converted with the same factor this page uses.