Deals with a general sizing equation for incompressible fluid flow under installed conditions. Factors are introduced which permit accurate sizing when choked conditions exist due to either cavitation or flashing. Procedures and factors are incorporated to handle installations where the valve is installed between fittings such as reducers, expanders, etc. A Reynolds number factor allows for applications where non-turbulent flow conditions exist caused by low differential pressure and/or high viscosity fluids. Numerical constants are presented permitting the use of three recognized flow coefficients: Av, Kv, and Cv.