# Dictionary:Filtration rate

${\displaystyle V={\frac {q}{A}}=-{\frac {k}{\mu }}\nabla P}$,
where ${\displaystyle \nabla P}$ is the pressure gradient, k the permeability, and ${\displaystyle \mu }$ the viscosity. The apparent filtration rate in a porous medium is ${\displaystyle V={\frac {q}{\phi }}A}$, where ${\displaystyle \phi }$ is the porosity.