[apache]

Well, I looked up planet surface gravity, and all kinds of other stuff just to find out where you got your information. Yes, I did find plainly given stats that claimed the surface gravity compared to earth's surface gravity. Now, I calculated through the numbers using the universal law of gravitation, and the maximum radius of Jupiter. This gives the aforementioned statistics that Jupiter's surface gravity is approximately 2.5 times that of earth's. However, the fact is that the 'surface gravity' here is the gravity at Jupiter's outer atmosphere. We don't know where the surface of Jupiter actually lies, and as such, using such a statistic to calculate gravity at the 'surface' of jupiter is pretty ridiculous. If Jupiter had a solid core the size of earth, for example, the gravitational acceleration there would be about 3520 times that of Earth's.
Oh, and I still have no idea where you found that gravity is some function of density, because its absolutely untrue. It is a function of mass and distance only. This is related by the equation, a=GM/(r^2) where M is the mass of the planet in kilograms, r is the distance from the center of that planet in meters, and G is the univerersal gravitational constant, 6.672*10^-11. This gives you the acceleration due to gravity.