The density of a substance is its mass per unit volume. the coherent SI unit of density is the kilogram per cubic meter(kg/m3) and the symbol designation used in this paper is p(Rho). Other commonly used metric units are: gram per cubic centimeter(g/cm3) or gram per millilitre(g/ml) 1g/cm3= 1 g/ml = 1000kg/m3

the coherent SI unit of specific volume V,which is the reciprocal of density,is the cubic metre per kilogram(m3/kg)