In fluid dynamics, the volumetric flux is the rate of volume flow across a unit area (m ·s), and has dimensions of distance/time (volume/(time*area)) - equivalent to mean velocity. The density of a particular property in a fluid's volume, multiplied with the volumetric flux of the fluid, thus defines the advective flux of that property. The volumetric flux through a porous medium is called superficial velocity and it is often modelled using Darcy's law.