Density is defined as the mass per unit of volume. It basically depends on how closely the atoms are spaced in a particular object or liquid. If the object floats on water, it means the the density of the object is lesser then the density of water, and if the object sinks, it means that its density if more than that of water. The density of a particular object or liquid is measure in g/cm3. In case of ethanol, its average density is 0.789 g/cm3 at the temperature of 20C. Density of Ethanol at Various Temperatures Here is a table which will give you more information about how the density of ethanol changes with the change in temperature and pressure of the surroundings.