air permeability diameter testing

Air Permeability Diameter

Air permeability via sub-sieve sizer is a classical analytical technique used to determine average particle size via water manometer. This technique is generally used for griseofulvin, metallurgical powders, and in the cement industry.

The true density (more information here) of the material must be known prior to analysis. Powder sample (equal in mass to the density) is packed into a column and subjected to regulated air flow. The pressure drop across the column is a function of permeability of the packed sample bed, which can be related to an average particle size, or “Fisher Number.” This assumes the sample consists of perfectly spherical particles. The analysis is performed twice and an average is reported.

The Fisher Sub-Sieve Sizer tests powders quickly and reproducibly for their Average Particle Diameter – also known as the Air Permeability Diameter.

Read More>


  • Conforms to ASTM STANDARD B330-20.
  • Conforms to USP Monograph for Griseofulvin.


  • This technique does not give particle size distribution information.
  • Density of the sample must be provided or determined prior to calculation of average particle diameter.

Sample Requirements

For griseofulvin, no less than 5 g of sample should be submitted.

For other samples, the required sample mass is dependent on the material’s true density. This analysis requires a mass twice (2x) the true density of the material, though higher quantities are recommended.

For additional questions on your sample needs, please contact us to share specifics about your sample and options for suitable sample quantities.

Detection Range

Covers a nominal particle size span of about 0.2 µm to 50 µm.

Data Reported

Tabulated data summary including:

• Porosity
• Average particle diameter (aka Fisher Number)
• Fisher calculated specific surface area