Black hole size calculator
Find how small a mass would have to be squeezed to become a black hole, or the mass of a black hole of a given size.
That's about the same as a 10-solar-mass black hole. As a black hole its event horizon would be 29.53 km in radius.
What it means
How massive is that?
Non-rotating (Schwarzschild) black hole. Spinning black holes have a smaller event horizon, down to half for maximum spin.
Every unit
That black hole in every unit
Learn
Three things worth knowing
-
3 km per Sun
Radius ≈ 2.95 km × solar masses: 10 Suns → 30 km, a million → 3 million km.
-
A letter from the front
Karl Schwarzschild found the solution in 1915, weeks after Einstein published general relativity, while serving in the German army.
-
Bigger is less dense
Average density inside the horizon falls with mass squared: a supermassive black hole can be less dense than water.
Shortcuts
Popular mass conversions
Background
About the Schwarzschild radius
Any mass squeezed inside its Schwarzschild radius, r = 2GM ÷ c², becomes a black hole: not even light escapes. The radius grows in step with the mass: 2.95 km per solar mass. The Earth would have to fit in 9 mm.
The black hole at the centre of our galaxy, Sagittarius A*, has 4.3 million solar masses and a radius of about 12.7 million km.