Visit my free, online MMAD and GSD calculator for aerodynamic particle size distribution for cascade impactor experiments. The calculator accommodates Andersen cascade impactors, Next Generation Impactors (NGIs), and Marple Miller impactors.

Mass Median Aerodynamic Diameter (MMAD) is the diameter at which 50% of the particles by mass are larger and 50% are smaller. United States Pharmacopeia (USP) <601> calls for determining the MMAD by plotting, on log probability paper, the percentages of mass less than the stated aerodynamic diameters versus the aerodynamic diameters. The MMAD is the intersection of the line with the 50% cumulative percent. Computational methods are often used.

Geometric Standard Deviation (GSD) is a measure of the spread of an aerodynamic particle size distribution. It’s typically calculated as follows:

GSD = (d84/d16)1/2

where d84 and d16 represent the diameters at which 84% and 16% of the aerosol mass are contained, respectively, in diameters less than these diameters.

MMAD GSD Calculator