 This equation can be expressed as ""flow is proportional to the pressure drop and inversely proportional to the fluid viscosity"", which is known as Darcy's law.Combining these equations gives the final Kozeny equation for absolute (single phase) permeability


The combined proportionality and unity factor formula_15 has typically average value of 0.8E6 /1.0135 from measuring many naturally occurring core plug samples, ranging from high to low clay content, but it may reach a value of 3.2E6 /1.0135 for clean sand.The denominator is included explicitly to remind us that permeability is defined using [atm] as pressure unit while reservoir engineering calculations and reservoir simulations typically use [bar] as pressure unit.