Schwarzschild Radius Calculator

The Schwarzschild radius is calculated using the formula Rs = 2GM/c², where G is the gravitational constant (6.674 × 10⁻¹¹ m³ kg⁻¹ s⁻²), M is the mass of the object, and c is the speed of light (≈ 3 × 10⁸ m/s). Simply multiply twice the gravitational constant by the object's mass, then divide by the speed of light squared. This calculator does all of that automatically once you enter the mass.

A 10 solar mass star has a Schwarzschild radius of approximately 29.5 kilometers. This means if that star were compressed to a sphere smaller than ~29.5 km in radius, it would collapse into a black hole. Most stellar black holes observed have masses between 5 and 20 solar masses.

Earth's Schwarzschild radius is approximately 8.87 millimeters — roughly the size of a marble. This means Earth would need to be compressed to less than 9 mm in radius to become a black hole. Of course, no natural process compresses planets to that density; only extremely massive stars can undergo such collapse.

Yes. The Schwarzschild radius defines the event horizon — the boundary beyond which nothing, not even light, can escape. The actual singularity of a black hole (where mass is concentrated) is theoretically a point of zero size at the center. The event horizon is not a physical surface but a mathematical boundary in spacetime.

For a non-rotating, uncharged black hole (a Schwarzschild black hole), the event horizon and the Schwarzschild radius are exactly the same thing. The event horizon is the spherical surface at distance Rs from the center where the escape velocity equals the speed of light. Objects and radiation that cross inward past this boundary can never return.

Yes — every object with mass has a theoretical Schwarzschild radius, including you. For a human of about 70 kg, the Schwarzschild radius is roughly 10⁻²⁵ meters, far smaller than a proton. The Schwarzschild radius only becomes physically meaningful when an object is actually compressed to that size, which only occurs in the death of very massive stars.

The surface gravity at the event horizon is given by g = GM/Rs², which simplifies to g = c⁴/(4GM). Paradoxically, for supermassive black holes the gravity at the event horizon can be relatively mild — a person falling into a billion-solar-mass black hole might not immediately notice crossing the event horizon, because tidal forces are weak at that scale.

The Sun's Schwarzschild radius is approximately 2.95 kilometers (about 1.83 miles). The actual Sun has a radius of ~696,000 km, so it would need to be squeezed to less than 3 km across to become a black hole. The Sun will never do this naturally — it lacks sufficient mass; it will instead end its life as a white dwarf.