Your question is probably based on the often quoted statement that if Saturn were placed in a body of water large enough, it would float. That is based on its average density, calculated by dividing total mass by volume. Archimedes' principle tells us that a body will float in a fluid if its average density is less than the fluid's average density. Since water's density is 1 gm/cm³, and Saturn's average density is 0.7 gm/cm³, a sphere of the same size and mass would float on water. Jupiter's average density is 1.4 gm/cm³, so a sphere of its size and mass would sink.