General Relativity is our current best theory of gravity, so I'll refer you to my post #47 on this thread.
I find it interesting that my original intent was to include "density" in my description..
( .. function of the density of mass.. )
While the short outline definition of Stress-Energy Tensor mentions "density" of energy and momentum...
Also "Newton's gravitational constant"..
More reading/study.. although I think that will be a dead end for what I'm trying to understand..