The pore space of soil contains the liquid and gas phases of soil, i.e., everything but the solid phase that contains mainly minerals of varying sizes as well as organic compounds.

In order to understand porosity better a series of equations have been used to express the quantitative interactions between the three phases of soil.

Macropores or fractures play a major role in infiltration rates in many soils as well as preferential flow patterns, hydraulic conductivity and evapotranspiration. Cracks are also very influential in gas exchange, influencing respiration within soils. Modeling cracks therefore helps understand how these processes work and what the effects of changes in soil cracking such as compaction, can have on these processes.

The pore space of soil is the habitat of plant roots (rhizosphere), soil fauna and microorganisms, and in turn growing plant roots and burrowing soil animals affect it by creating networks of interconnected pores.

The dry bulk density of a soil greatly depends on the mineral/organic assemblage making up the soil and on its degree of compaction. The density of quartz is around 2.65 g/cm³ but the dry bulk density of a soil can be less than half that value.

Most soils have a dry bulk density between 1.0 and 1.6 g/cm³ but organic soils may have a dry bulk density well below 1 g/cm³.

Core samples are taken by pushing a metallic cutting edge into the soil at the desired depth or soil horizon. The soil samples are then oven dried (often at 105 °C) until constant weight.

The dry bulk density of a soil is thus inversely proportional to its porosity. The more pore space in a soil, the lower its dry bulk density.