For a material with unknown density (i.e., mass per unit volume, ρ, in kg/m³ rarely more than the simplest facts will be available. Thus these have to be taken as the basis for deriving an estimated density.

A. Metal alloys

The densities of the pure metals are related to their places in the Periodic table but are not strictly parallel to their atomic masses. The density of alloys can be estimated as the composed density according to the mass fractions of the single elements in the alloy:

\[\label{eq1} \rho_A=\dfrac1{x_1/\rho_1+x_2/\rho_2+x_3/\rho_3} \tag{1}\]

where ρ_i is the density of the single component and ρ_A the density of the alloy.