A cubic means having three dimensions in the solid state.
As a guide it is easy to compare weight and cubic metres of water and so; 1 cubic meter of water weighs one metric ton ( 1000kg). The density of wood can vary so much eg balsa is so light perhaps 150kg per cubic metre and ebony perhaps 2000kg. The only real answer is that you need to know what sort of wood and then work out with a small test (displacement) what the mass is. If you sink the wood in to water and collect the water you can work out the mass, weigh the wood and you have the answers.... simples
The specific gravity of cast iron typically ranges from 6.9 to 7.8. This value may vary depending on the composition and metallurgical properties of the specific type of cast iron. It is a measure of how dense the material is compared to water.