What's earth's gravity ?

Gravity is caused by mass. The more mass that a body possesses, the stronger it's gravitational pull. All objects create gravity, including you and me, it is just on a much smaller scale than a larger body such as Earth. But, size is not the only factor in creating mass, the density is important, too. A black hole, for instance, created by an imploding star, is not necessarily a large object, but will suck objects in and crush them that reach within a certain distance. That is because the star collapses into itself creating a super dense structure. So, in order to create the most gravity, the goal would be to create a very dense object, that which does not exist on Earth, and is beyond our current scientific capability.