🕳️ Schwarzschild Radius Calculator
Enter a mass to get its Schwarzschild radius: how small it would have to be squeezed to become a black hole.
Schwarzschild radius
2.954 km
Event-horizon diameter
5.908 km
The Schwarzschild radius is how small a mass must be squeezed to become a (non-rotating) black hole — the radius of its event horizon: r = 2GM ÷ c². It works out to about 2.95 km per solar mass, so the Sun would need to collapse to under 3 km across, and the whole Earth to about 9 mm. 🔒 In your browser.
How the schwarzschild radius calculator works
The Schwarzschild radius is the radius of the event horizon of a non-rotating black hole of a given mass: r = 2GM ÷ c², where G is the gravitational constant and c the speed of light. Because c² is enormous, the radius is tiny — about 2.95 km per solar mass. Squeeze any mass inside its Schwarzschild radius and not even light escapes. The tool takes a mass in solar masses, Earth masses or kilograms and shows the radius (and event-horizon diameter) in sensible units.
This is the classic result for a spherical, non-rotating (Schwarzschild) black hole. Real black holes usually spin, which shrinks the horizon slightly (the Kerr solution), but the Schwarzschild radius is the standard reference size and a good order-of-magnitude guide.
Frequently asked questions
What is the Schwarzschild radius?
The radius at which a mass becomes a black hole — the size of its event horizon. Compress a mass within this radius and its escape velocity exceeds the speed of light, so nothing, not even light, can escape. It's r = 2GM ÷ c².
How do I calculate the Schwarzschild radius?
r = 2GM ÷ c², with G = 6.674×10⁻¹¹, c = 3×10⁸ m/s and mass in kilograms. A handy shortcut: the radius is about 2.95 km for every solar mass, so a 10-solar-mass black hole is roughly 30 km across.
What is the Schwarzschild radius of the Sun?
About 2.95 km. If the Sun (which is 1.4 million km across) were crushed into a sphere under 3 km in radius, it would become a black hole. Our Sun won't — it isn't massive enough to collapse that far.
What is the Schwarzschild radius of the Earth?
About 8.9 mm — smaller than a marble. That's how much you'd have to compress the entire Earth to make it a black hole, which is why stellar-mass black holes require the collapse of very massive stars.
Do real black holes match the Schwarzschild radius?
For non-rotating ones, yes. Most real black holes spin, described by the Kerr solution, which makes the horizon a bit smaller than the Schwarzschild value. The Schwarzschild radius remains the standard baseline size for a given mass.