Since the mass of a particle is proportional to its class, the total mass of a particle population can be calculated as :

(8–4)

Note that is the mass of a bulk species molecule comprising the particle core and is constant. The total mass of a particle population can be expressed in a simple form as Equation 8–5 .

(8–5)

Here,

is the first moment of the discrete particle-size distribution function . The average particle mass of the population can be obtained by dividing the total particle mass by the number of particles and is given in Equation 8–6 ,

(8–6)

where is the average particle class of the population.