🕳️Schwarzschild Radius Calculator
Find the event horizon radius of any mass — pick a preset or enter a custom mass in kilograms or solar masses.
Free Schwarzschild Radius Calculator
Curious how small a black hole really is? Our free Schwarzschild Radius Calculator finds the event horizon radius of any mass using r = 2GM/c², the formula from general relativity that defines a black hole's boundary. Pick a preset — Earth, the Sun, or even the supermassive black hole at our galaxy's center, Sagittarius A* — or enter a custom mass in kilograms or solar masses.
Alongside the number, you'll get a plain-English explanation of what it means: compress Earth down to about 9 millimeters, or the Sun to roughly 3 kilometers, and either would collapse into a black hole. It's a great way to build real intuition for how gravity and density relate.
No sign-up, no downloads, no limits — just clear results whenever you're curious. See the About page or the FAQ for more.