All things with mass or energy cause curvature of spacetime. The amount of curvature depends on the amount of mass/energy and the distance from it. Unfortunately I do not know the math to calculate all that.
Black holes are very special in that the only qualities they possess are mass, charge, and angular momentum. If you know the value of those three qualities, you can calculate everything else about them, including their surface gravity. For the simplest case, a black hole with no charge and no angular momentum (i.e. non-rotating), the http://en.wikipedia.org/wiki/Surface_gravity#The_Schwarzschild_solution" provides a simple result.
Astronomers have observed black holes with masses of 18 billion times that of the Sun; you can plug that value into the Schwarzschild solution and compute the gravitational "strength" of the largest black holes known.