About this tool
The Stellar Parallax Distance Calculator is a free, in-browser astronomy tool that converts a star's trigonometric parallax into its distance and back. The relation is beautifully simple: distance in parsecs equals the reciprocal of the parallax in arcseconds, d(pc) = 1 / p(″). The parsec is defined precisely so this holds — a star with a parallax of one arcsecond lies one parsec away.
Everything is calculated locally in your browser, so nothing you enter is sent anywhere. Leave either the parallax or the distance blank and the tool fills in the other. Parallax can be entered in arcseconds or milliarcseconds (mas), the unit used by modern surveys like Hipparcos and Gaia, where nearby stars have parallaxes of only a few to a few hundred milliarcseconds.
The distance is reported in parsecs, light-years (1 pc ≈ 3.2616 ly), and astronomical units (1 pc ≈ 206,265 AU) so you can express it on whatever scale you need. As a worked example, a parallax of 0.1″ corresponds to a distance of 10 parsecs, which is about 32.6 light-years.