🕳️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.
About the Schwarzschild Radius Calculator
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.
Frequently Asked Questions
What is the Schwarzschild radius?
The radius to which a mass must be compressed for its escape velocity to equal the speed of light, forming a black hole's event horizon.
How does this calculator work?
Pick a preset body or enter a custom mass in kg or solar masses, and it computes the radius instantly using r = 2GM/c².
Is it free?
Completely free, no sign-up, downloads, or limits.
What is Earth's Schwarzschild radius?
About 8.87 millimeters — roughly the size of a peanut.
What is the Sun's Schwarzschild radius?
About 2.95 kilometers.
Does a bigger mass mean a bigger black hole?
Yes, the Schwarzschild radius scales linearly with mass — more mass means a proportionally larger event horizon.
Can I enter mass in solar masses?
Yes, there's a unit toggle between kilograms and solar masses.
What happens if I enter a negative or zero mass?
The calculator rejects it with a clear validation message.
Is my data stored?
No; everything runs in your browser and isn't stored or sent anywhere.
Does it work on mobile?
Yes, fully responsive on all screen sizes.