About the Schwarzschild Radius Calculator
Find the event horizon radius of any mass, from Earth to a supermassive black hole.
What it is
The Schwarzschild radius, r = 2GM/c², is the radius a mass would need to be compressed within for its escape velocity to reach the speed of light — the defining boundary of a black hole's event horizon. This tool computes it for planets, stars, and black holes, or any custom mass you enter.
Features
Planet, star & black hole presets
Earth, Jupiter, the Sun, a stellar-mass black hole, and Sagittarius A*.
Custom mass input
Enter any mass in kilograms or solar masses with a unit toggle.
Formula shown
The full r = 2GM/c² substitution with your actual entered values.
Plain-English explanation
What the number means and how it compares to Earth and the Sun.