What is the order of most dense to least with solids, liquids and gases?

Solids are denser than liquids, and liquids are denser than gases at room temperature. Solids are atoms and molecules in a relatively motionless crystal lattice configuration. Liquids are comprised of molecules with more energy and aren't confined to a lattice. Gases are high energy, and their molecules are spaced apart.

Pressure and heat factor into the densities of these states of matter. If a gas isn't under pressure, the atoms and molecules fly away from each other. Increasing the temperature of a solid gives the molecules enough energy to break free of the crystal lattice and move like a liquid. Adding even more heat makes the liquid less dense, and turns it into a gas.