Scaling-up of filtration systems in the pharmaceutical industry to provide the correct filtration capacity is a complex process. When several filters are used in parallel, the pressure and flow distribution within the system can be modeled using well-established constitutive laws to a high degree of accuracy, as shown in this paper. By combining the model with experimental fouling data, it is also possible to accurately predict the flow and pressure distribution during an entire filtration run. A process is discussed that uses this model to determine how the capacity of a filtration system can be accurately predicted using a minimal set of measurements.