Schwarzschild Radius Calculator (Black Hole Event Horizon)
Enter the mass to find the radius of the event horizon.
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Schwarzschild Radius Calculator (Black Hole Event Horizon) by TheCalcTools
How the Schwarzschild Radius Calculator (Black Hole Event Horizon) works
A mass compressed within its Schwarzschild radius r = 2GM/c² becomes a black hole; nothing, not even light, can escape from inside. The calculator uses the IAU nominal solar value GM☉ = 1.32712440018 × 10²⁰ m³/s².
The radius grows in proportion to mass: about 2.95 km per solar mass. Earth would have to be squeezed into about 9 mm.
The formula
Worked example
Using the default values shown in the calculator:
| Mass given in | Solar masses |
|---|---|
| Mass | 10 |
- A 10 solar-mass black hole has a Schwarzschild radius of 29.5325 km.
Result:
| Schwarzschild radius (km) | 29.5325 |
|---|---|
| In metres | 29532.5 |
| Diameter (km) | 59.0650 |
| Average density inside (kg/m³) | 184300000000000000 |
Frequently asked questions
How big is the black hole at the centre of our galaxy?
Sagittarius A* has about 4 million solar masses, so its Schwarzschild radius is roughly 12 million km.
Sources and further reading
- Wikipedia: Schwarzschild radius
- IAU: Resolution B2 (2012) on the astronomical unit and B3 (2015) on nominal solar values
- NIST CODATA: Fundamental physical constants
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.