Find two empty beakers, one big and one small. Put the small beaker in the big beaker. Fill the beaker with water. Put it on the water, the cup surface of the small beaker is flat. Be careful not to drip into the big beaker.

First measure the weight of the stone, assuming it is a.

Gently put the stone into the small beaker, and the water overflows into the big beaker. Measure the weight of water in the beaker, and calculate the volume of overflow water, that is, the volume of stone, according to the density of water (1ml/mg). Suppose it's B.

B divided by a is the density of the stone.