Parallax Distance Calculator
Find a star's distance from its parallax angle.
Results update as you type.
How it works
Parallax is the most direct way to measure the distance to nearby stars, and this calculator converts a parallax angle into a distance. You enter the parallax angle in arcseconds, and it returns the distance in parsecs and light-years. Stellar parallax is the small apparent shift in a star's position when viewed from opposite sides of Earth's orbit around the Sun, six months apart. Nearer stars shift more, and this angle, measured in tiny fractions of a degree called arcseconds, reveals the distance. The relationship is beautifully simple because of how the parsec is defined: distance in parsecs equals one divided by the parallax in arcseconds. A star with a parallax of one arcsecond is one parsec away, and the word parsec itself comes from parallax of one arcsecond. Smaller parallax angles mean more distant stars, so a parallax of 0.1 arcseconds corresponds to ten parsecs. The calculator also converts to light-years, with one parsec equal to about 3.26 light-years. Parallax is the foundation of the cosmic distance ladder, providing the direct geometric measurements that calibrate all other distance methods. Space missions like Hipparcos and Gaia have measured parallaxes for millions of stars with extraordinary precision. The parallax angle must be positive. Enter the parallax to find the star's distance.
d (parsecs) = 1 / p (arcseconds)
Stellar parallax is the tiny apparent shift of a nearby star against distant background stars as Earth orbits the Sun. The distance in parsecs is simply the reciprocal of the parallax angle in arcseconds. The parsec is defined so that a parallax of one arcsecond corresponds to exactly one parsec.
Source:Astronomy
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter parallax angle.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Distance updates instantly as you type — no button to press.
Frequently asked questions
What is stellar parallax?
Stellar parallax is the apparent shift in a nearby star's position against distant background stars as Earth moves around the Sun. Observed six months apart from opposite points in Earth's orbit, closer stars appear to shift more. Measuring this tiny angle allows astronomers to calculate the star's distance directly through geometry.
How does parallax give distance?
The distance in parsecs equals one divided by the parallax angle in arcseconds. This simple reciprocal relationship exists because the parsec is defined as the distance producing a parallax of exactly one arcsecond. A smaller parallax means a more distant star, so measuring the angle immediately yields the distance.
What is a parsec?
A parsec is a unit of distance equal to about 3.26 light-years, or roughly 31 trillion kilometers. Its name comes from parallax of one arcsecond, the distance at which a star shows a parallax of one arcsecond. The parsec is the standard distance unit in professional astronomy, more natural than light-years for parallax work.
Why can parallax only measure nearby stars?
Parallax angles shrink with distance, becoming immeasurably small for far-away stars. Even the nearest stars have parallaxes below one arcsecond, and beyond a few thousand parsecs the angle is too tiny to measure accurately from the ground. Space telescopes like Gaia extend the reach, but parallax remains limited to the nearer parts of our galaxy.
Why is parallax important in astronomy?
Parallax provides the only direct, geometric measurement of stellar distances, requiring no assumptions about a star's brightness. It anchors the cosmic distance ladder, calibrating indirect methods like standard candles used for farther objects. Precise parallax surveys by missions such as Gaia have transformed our knowledge of the structure and scale of the Milky Way.