Find the mass of a black hole from just its radius?

[Lamdbaenergy]

I know the original schwarzschild formula for finding the radius of the black hole, but what equation can be used to find its mass if you ONLY know its radius?

 

[Bandersnatch]

Can't you use the same formula? Only instead of using mass to find the Schwartzschild radius, use the Schwartzschild radius to find the mass.

 

[Lamdbaenergy]

Can't you use the same formula? Only instead of using mass to find the Schwartzschild radius, use the Schwartzschild radius to find the mass.

Nope, got nowhere near the right mass. I tried for a solar mass black hole, too. Any other suggestions?

 

[Bandersnatch]

Can you show what you did exactly?

 

[Lamdbaenergy]

Can you show what you did exactly?

2GR/c^2, then I tried R^2c^2/2G

 

[Bandersnatch]

Neither of those is correct. Start with the Schwartzschild radius formula $r_s=\frac{2Gm}{c^2}$ and isolate the mass on one side.

 

[syhprum1]

Here is a useful calculator that does it all for you
http://xaonon.dyndns.org/hawking/