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

(19–4)

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 19–5 .

(19–5)

Here,

(19–6)

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 19–7 ,

(19–7)

where is the average particle class of the population.