Schwarzschild Radius Calculator

It is the radius at which an object would have to be compressed for its escape velocity to equal the speed of light. Inside this radius not even light can escape, which defines the event horizon of a black hole.

If the entire Earth were crushed within its Schwarzschild radius, it would shrink to a sphere only about nine millimeters across. The Sun would need to collapse to a radius of roughly three kilometers.

For a non-rotating, uncharged mass, no. The formula r = 2GM/c² uses only the mass along with the fixed constants G and c, so the radius is directly proportional to mass. Rotation or charge would call for the more general Kerr or Reissner-Nordström solutions.

Plug the mass in kilograms into r = 2GM/c², using G = 6.674 × 10⁻¹¹ and c = 2.998 × 10⁸ m/s. For the Sun (M ≈ 1.989 × 10³⁰ kg): the numerator 2GM ≈ 2.655 × 10²⁰ divided by c² ≈ 8.988 × 10¹⁶ gives about 2,950 m, or 2.95 km. Because the radius scales linearly with mass, you can also shortcut it as roughly 2.95 km per solar mass. Sagittarius A*, the supermassive black hole at the center of the Milky Way, is about 4.3 million solar masses, giving a Schwarzschild radius near 12.7 million km, about 18 times the radius of the Sun itself.