Certainly - all matter has density. The density of a gas planet would probably be less than that of a more solid planet but it would still have a non-zero density.
Saturn has the lowest density of any planet, terrestial or gas giant.
All the gas giants; in our Solar System, Saturn has the lowest density (less than the density of water).
Density of a planet = (Planet's mass) divided by (Planet's volume)
Parameters such as mass, radius, and density can provide clues about a planet's composition. For example, a high density suggests a rocky composition, while a low density suggests a more gas-rich composition. Additionally, spectroscopy can be used to analyze the planet's atmosphere and determine the presence of certain elements or compounds.
a gas planet
Saturn is the least dense of the gas giants, even out of all of the planets in our solar system. Its average density is around 0.7 g/cc (less than water).
A planet composed mostly of gas is less dense than a rocky planet. The gas planets of our solar system range in density from 0.69-1.6 g/cm^3. By comparison the terrestrial planets have densities of 3.9-5.5 g/cm^3
Mercury has the second lowest density of any planet in the solar system. Saturn has the lowest density of any other planet.
The phrase "least dense planet" refers simply to the planet with the lowest density, which is the planet's mass divided by its volume. In our solar system, Saturn is the least dense planet with a density of roughly 0.7 (water, by comparison, has a density of 1, or 1 gram per cubic centimeter). This is attributed to its large outer envelope of gas - although it is thought to have a denser rocky core.
Earth's density: 5520 kg/m3 Saturn's density: 690 kg/m³
The planet with the lowest overall density is Saturn.
Saturn is a planet made out of mostly gas. As gas has little mass, it is less dense than Earth. Remember that density is proportional to its mass and surface area.