# Calculation Methods - User Defined Generic

The general 3 term equation relating pressure loss to flow is defined as ΔP = K + A B Qn + C D Qm where K, A, B, C, D, n and m are constants (fixed values) or an inlet property (either density, viscosity or pressure) and Q is the flowrate. By setting the K, A, B, C and D terms there are many loss equations possible. For example a simple fitting may have a pressure loss that is proportional to flow squared. To achieve this equation all we need to do is set the K term and either the C or D term to zero. This will reduce the equation to ΔP = A B Qn , so if we set A = 1, B equal to the constant of proportionality and n to 2 we arrive at the equation we want.