Here are the approximate densities of the eight planets of the solar system, measured in grams per cubic centimetre.

Earth 5.51

Mercury 5.43

Venus 5.24

Mars 3.94

Neptune 1.76

Jupiter 1.33

Uranus 1.27

Saturn 0.69

There is a clear break between the top four (known as the 'terrestrial' planets) and the rest. The top four are composed of silicate rocks and metals and have a solid surface. Jupiter and Saturn are gas giants; Uranus and Neptune are ice giants.

To get a feel for the density scale, the density of water is (approximately) 1.00 gram per cubic centimetre. This means that the Earth is more than five-and-a-half times as dense as water. But, at the other end of the scale, Saturn's density is less than seventy percent that of water. A scaled-down Saturn would float on your swimming pool, beach-ball style.

More Info: