The best number to begin with is the density of water: 1 g per cubic centimeter.
The density of other common materials can be found on many Web sites by Googling "density"
By "Relative density" you may be thinking of "specific gravity" which is the density relative to water. For example, lead metal has a density of 11.6 g per cc. Its specific gravity is = 11.6 g per cc/ 1 g per cc = 11.6. This means that it is 11.6 times denser than water.
What is the specific gravity of copper metal whose density is 7.9 g per cc? It is 7.9! It is 7.9 times as dense as water.
What is the specific gravity of ethyl alcohol which as a density of .85 g per cc? .85. It is .85 or 85% the density of water.
I don't know what you mean by "volume".