MMAD Calculator is a free, web-based application that calculates the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) for an aerodynamic particle size distribution determined with an Andersen cascade impactor (ACI), Next Generation Impactor (NGI), or Marple Miller impactor. See the Calculations page for details on the methodology used.

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MMAD & GSD Calculator for Marple Miller Impactors


1) Select the flow rate through the cascade impactor from the drop-down menu below.
2) Enter the mass collected on each impactor stage in the highlighted fields, using your mouse to navigate to the next highlighted field. After entering the last value, click on any other highilghted field to complete the calculation.

NOTE: The algorithm does not check that your distribution is log-normal, but you can get a sense of that from the graph below. To view the graph, Macromedia Flash must be installed on your computer.

Select Flow Rate:
Impactor Cutoff Diameter
Stage (microns) Drug Collected
Stage 1
Stage 2
Stage 3
Stage 4
Stage 5
Filter n/a
MMAD: microns
Excel spreadsheet to Html form