The measurement involves injection of mercury, a non-wetting liquid, into the sample whose porosity is to be measured. The hydraulic pressure applied for injection of mercury into the sample is inversely proportional to the pore radius in the sample in accordance with  Washburn’s law.

Analysis requires solid samples. Materials with high porosity (greater than 35%) require small quantities of the sample (0.2 - 0.3 gm.) while materials with low porosity require large amounts of sample (2 – 3 gm.)