The amount of space an object occupies is its volume. Volume is not always a fixed measurement. For any given object, volume is likely varies depending on pressure and temperature.
Usually volume is not directly measured, but rather derived by multiplying length times depth times width. The volume of an irregularly shaped object derives through displacement, or dropping it in water and measuring how much water it displaces.
Objects subjected to high pressure or low temperature tend to have a smaller volume, while heated objects tend to have a larger volume. Travel in space or the deep ocean must account for this, as the enormous difference in pressure inside versus outside a space ship or submarine can cause the vehicle to explode or implode.