Before revision: It is a dimensionless quantity in materials science and in soil science, and is closely related to the porosity (often noted as , or , depending on the convention), the ratio of the volume of voids () to the total (or bulk) volume (), as follows: in which, for idealized porous media with a rigid and undeformable skeleton structure (i.e., without variation of total volume () when the water content of the sample changes (no expansion or swelling with the wetting of the sample); nor contraction or shrinking effect after drying of the sample), the total (or bulk) volume () of an ideal porous material is the sum of the volume of the solids () and the volume of voids ():
After revision: (in a rock, or in a soil, this also assumes that the solid grains and the pore fluid are clearly separated, so swelling clay minerals such as smectite, montmorillonite, or bentonite containing bound water in their interlayer space are not considered here.)It is a dimensionless quantity in materials science and in soil science, and is closely related to the porosity (often noted as , or , depending on the convention), the ratio of the volume of voids () to the total (or bulk) volume (), as follows: in which, for idealized porous media with a rigid and undeformable skeleton structure (i.e., without variation of total volume () when the water content of the sample changes (no expansion or swelling with the wetting of the sample); nor contraction or shrinking effect after drying of the sample), the total (or bulk) volume () of an ideal porous material is the sum of the volume of the solids () and the volume of voids ():