Parallax Distance Calculator
Enter a star's annual parallax angle in arcseconds to get its distance in parsecs — plus the equivalent in light-years — using the simple relation d = 1 / p.
Parsecs and light-years at once
Enter the parallax angle in arcseconds and the calculator returns the distance in parsecs (1 ÷ p) and the same distance in light-years together.
Use arcseconds
The parallax must be in arcseconds. A smaller angle means a more distant star, so a parallax of 0.1 arcsec puts the star 10 parsecs away.
What is parallax distance?
The reciprocal of the parallax angle
This parallax distance calculator turns a star's measured annual parallax into how far away it lies. Parallax is the tiny apparent shift of a nearby star against the distant background as the Earth moves around the Sun. Astronomers measure that shift as an angle, and because the geometry is fixed, the distance is simply the reciprocal of the angle: a star whose parallax is one arcsecond sits exactly one parsec away. The calculator takes a single input — the parallax angle in arcseconds — and returns the distance in parsecs and in light-years. It is the foundation of the cosmic distance ladder and the most direct way astronomers know how far the nearest stars really are.
Enter a parallax angle in arcseconds to get the distance in parsecs and light-years instantly.
The distance in parsecs is the reciprocal of the parallax angle in arcseconds, and the distance in light-years is the parsecs multiplied by 3.26156.
d = 1 / pBecause distance is one over the angle, halving the parallax doubles the distance: a parallax of 0.05 arcsec puts a star 20 parsecs away. To express the result in light-years, multiply the parsecs by 3.26156, the number of light-years in one parsec. Worked example: a star with a parallax of 0.1 arcsec lies 1 ÷ 0.1 = 10 parsecs away, which is 10 × 3.26156 = 32.6156 light-years.
The formula is exact, but parallax measurement has real practical limits.
Best for relatively nearby stars
Parallax distance is only practical for relatively nearby stars, where the shift angle is large enough to measure. Because distance is the reciprocal of the angle, distant stars produce vanishingly small parallaxes that are hard to pin down — ground-based telescopes are reliable to a few hundred parsecs, while space missions such as ESA's Gaia push the method to thousands of parsecs. The parallax must be a positive angle in arcseconds; a zero or negative value has no physical distance, and very tiny angles carry large uncertainty.