Schwarzschild Radius Calculator
Fill in the value and the answer updates as you type.
How the Schwarzschild Radius Calculator works
The Schwarzschild radius is where the escape speed equals the speed of light: r = 2GM ÷ c². It works out to about 2.95 km for each solar mass. The Sun would need to shrink to under 3 km to become a black hole. The average density falls as the mass grows, so a supermassive black hole can be less dense than water. The formula applies to a non-rotating black hole. Example: with Object mass 10 solar masses, the result is Schwarzschild radius (km) = 29.53; Schwarzschild radius (miles) = 18.35; Event horizon diameter (km) = 59.07.
Inputs and results
The Schwarzschild Radius Calculator takes 1 input and gives 4 results.
What you enter
- Object mass (solar masses) — starts at 10.
What you get
- Schwarzschild radius (km)
- Schwarzschild radius (miles)
- Event horizon diameter (km)
- Average density inside (kg/m³)
Example: Schwarzschild Radius Calculator with the starting values
With object mass 10 solar masses, the calculator returns:
| Schwarzschild radius (km) | 29.53 |
|---|---|
| Schwarzschild radius (miles) | 18.35 |
| Event horizon diameter (km) | 59.07 |
| Average density inside (kg/m³) | 184,285,159,959,822,100 |
Change any value above and the results update straight away.
Schwarzschild Radius Calculator FAQ
How do I use the Schwarzschild Radius Calculator?
Enter object mass in the fields, then read schwarzschild radius (km), schwarzschild radius (miles), event horizon diameter (km) and average density inside (kg/m³) in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Schwarzschild Radius Calculator calculate?
Event horizon size of a black hole from its mass. It returns schwarzschild radius (km), schwarzschild radius (miles), event horizon diameter (km) and average density inside (kg/m³) from the 1 value you provide.
What values does the Schwarzschild Radius Calculator start with?
It opens with object mass 10 solar masses so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Schwarzschild Radius Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Schwarzschild Radius Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.