Assuming the laminar flow across the filter, the rate of filtration (dVf/dt) can be expressed as a function of pressure drop Dp by the modified D'Arcy's equation as (where A is the area of filtering surface, K is the D'Arcy's filter cake permeability and L is the thickness of the filter cake)

• (1/A) dVf/dt = Δp/μ(L/K)
• dVf/dt = (1/A)Δp/μ(L/K)
• (1/A) dVf/dt = Δp/μ LK
• dVf/dt = (1/A)Δp/μ LK