Specific area
The specific area is the surface available for coating of a given quantity of product. It depends of the surface of each particle and number of particles in a volume : basically it depends of the average diameter. In other words, the smaller the particles, the more coating liquid they will require by unit of base product.
The relation between radius and specific area is given by a formule

Specific weight
Product specific weight is a key information in calculating the expected output of a process run on a volumetric coating system such as a drum, a screw.

To get the ouptut, multiply the specific weight by the machine volumetric output ; example : 120 g/L x 1000 L/h = 120 000 g/L = 120 kg/h.
Conversely, to size the machine, divide the required gravimetric output by the product specific weight ; example : (200 gk/H) / (0.4 kg/L) = 500 L/h