Porosimetry is an analytical technique used to determine various quantifiable aspects of a material's porous structure, such as pore diameter, total pore volume, surface area, and bulk and absolute densities.
The technique involves the intrusion of a non-wetting liquid (often mercury) at high pressure into a material through the use of a porosimeter.
The pore size can be determined based on the external pressure needed to force the liquid into a pore against the opposing force of the liquid's surface tension.
The contact angle of mercury with most solids is between 135° and 142°, so an average of 140° can be taken without much error.
With the various substitutions, the equation becomes: As pressure increases, so does the cumulative pore volume.