Black Hole Calculator
Example: Earth → 1.8 cm black hole
For an ideal non-rotating, uncharged black hole, Earth’s mass gives a Schwarzschild radius of about 8.9 mm, a 1.8 cm event-horizon diameter. Enter any positive mass to calculate this idealized radius. Real astrophysical black holes rotate, measured masses carry uncertainty, and the “uniform density” comparison is only mass divided by the volume inside the horizon, not a model of the interior.
Calculation results updated
Schwarzschild radius across masses
Schwarzschild Radius (idealized)
Density (if uniform)
Size Comparison
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How We Calculate This
For the non-rotating, uncharged Schwarzschild model, Rs = 2GM/c². This implementation uses the 2022 CODATA value G = 6.67430×10⁻¹¹ m³ kg⁻¹ s⁻² and exact SI value c = 299,792,458 m/s. The displayed average density is 3M/(4πRs³), a geometric comparison, not a claim that a black hole contains uniform ordinary matter.
Methodology last reviewed: July 2026. How SparkCalc works
Sources: NASA Science: Black Holes · NASA Imagine the Universe: Black Holes · NIST: CODATA Value: Newtonian Constant of Gravitation · NIST: CODATA Value: Speed of Light in Vacuum
Schwarzschild radii for familiar masses
Values use Rs = 2GM/c² for ideal non-rotating, uncharged black holes. Astronomical object masses are measured estimates.
| Mass | Schwarzschild radius | Event-horizon diameter |
|---|---|---|
| Earth | 8.87 mm | 1.77 cm |
| Sun | 2.95 km | 5.91 km |
| 10 solar masses | 29.5 km | 59.1 km |
| Sagittarius A* (~4.154 million Suns) | 12.3 million km | 24.5 million km |
| M87* (~6.5 billion Suns) | 19.2 billion km | 38.4 billion km |
A black-hole shadow is larger than the event horizon and should not be compared directly with these radii.
Frequently Asked Questions
What is the Schwarzschild radius?
It is the event-horizon radius for the ideal Schwarzschild solution: a non-rotating, uncharged black hole. The formula is exact within that model; applying it to planets, people or estimated astronomical masses is hypothetical or approximate.
Could Earth become a black hole?
The formula gives Earth an 8.9 mm radius, or about 1.8 cm across. This is a hypothetical scale comparison; no known natural process can compress Earth that way.
Why do larger black holes have lower density?
Schwarzschild radius scales linearly with mass (R ∝ M), but volume scales with radius cubed (V ∝ R³). So density ∝ M/R³ ∝ 1/M². Supermassive black holes have surprisingly low average densities, sometimes less than water!
What happens at the event horizon?
At the event horizon, escape velocity equals the speed of light. Nothing can escape once crossed. To an outside observer, objects appear to freeze at the horizon due to extreme time dilation.
Is TON 618 the largest known black hole?
TON 618 is a widely cited ultramassive quasar estimate near 66 billion solar masses, but “largest known” is not a stable or like-for-like title. Mass estimates depend on observational models, and other candidates have different or highly uncertain estimates.
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