⚠ Extreme Gravity — Do Not Approach

Black Hole Radius Calculator

a* = 0 means not spinning, 1 is the maximum spin, a negative value spins the other way. Try 0.9.

Constants: M☉ = 1.988416×10³⁰ kg · R☉ = 695,700 km
With spin: r₊ = (GM/c²)(1 + √(1 − a²))

Calculates the Schwarzschild radius, the boundary beyond which nothing, not even light, can escape, for any mass using R = 2GM/c². Enter a mass in solar masses, Earth masses, or kilograms to find its event horizon radius instantly. Press Add spin to include the spin of a rotating black hole: its event horizon is smaller than the Schwarzschild radius, r₊ = (GM/c²)(1 + √(1 − a²)).