A method for calculating availability in line power systems composed of power circuit modules determines power circuit parameters associated with the power circuits, accepting input from central databases. The method calculates a required number of power circuits to complete the line power system, and calculates the total power to be delivered over the power system, based on a power calculator. The method calculates individual power circuit availabilities based on the power circuit compositions and external variables. The method then calculates an overall system availability based on the power circuit availabilities and other external variable inputs. The method may compare the calculated line power system availability with a target availability, revise the power circuit parameters, and recalculate the system availability to meet the target availability.