Parsecs to Light years Converter

How many light years are in a parsec?

A parsec is about 3.2616 light years. The converter uses the constant 3.261563 and multiplies your parsecs by it, then rounds the answer to four decimal places.

light years = parsecs × 3.261563

For reference, the exact figure is 3.26156378 ly per parsec, so the value used here is short by about one part in four million. That is invisible at the four decimals the converter displays.

What a parsec and a light year measure

Both units measure distance, not time, even though the light year has "year" in its name. A light year is the length light covers in a vacuum in a Julian year of 365.25 days: 9,460,730,472,580,800 m, or about 9.46 trillion km.

A parsec (short for parallax of one arcsecond) is defined with an angle. Imagine a triangle whose short side is the Earth-Sun distance of 149,597,870,700 m (one astronomical unit). The parsec is the length of the long sides when the angle at the star is a single arcsecond, 1/3,600 of a degree. Doing the trigonometry gives about 3.0857 × 10¹⁶ m, which is where the 3.26 light year figure comes from.

Large-scale astronomy works in kiloparsecs (1,000 pc) for the Milky Way and megaparsecs (1,000,000 pc) for the space between galaxies. Multiply any of those by 3.261563 and by the right power of ten to get light years.

How to convert parsecs to light years

1. Enter the number of parsecs in the first box.
2. Read the light years in the second box. It refreshes with every keystroke.
3. For a manual check, multiply the parsecs by 3.261563.

Example 1. A star measured at 2.64 pc, which describes Sirius, is 2.64 × 3.261563 ≈ 8.6105 ly away.

Example 2. The Sun sits roughly 8 kpc from the center of the Galaxy. That is 8,000 pc × 3.261563 ≈ 26,092.5 ly.

Example 3. A galaxy at 0.78 Mpc is 780,000 pc away, and 780,000 × 3.261563 ≈ 2,544,019 ly, close to the distance usually given for Andromeda.

Parsecs to light years conversion table

Common slips

• Dividing instead of multiplying. Parsecs are the bigger unit, so the number of light years must come out larger than the number of parsecs.
• Forgetting the prefix. A distance of 12 kpc is 12,000 pc, not 12 pc, before you convert.
• Treating the light year as a time. It is a distance of about 9.46 trillion km.

To work from light years instead, use the light years to parsecs converter. The physics converters page lists other unit tools, and the time dilation calculator is a related physics topic for very fast travel.