Electrical energy calculations The amount of electrical energy transferred to an appliance depends on its power and the length of time it is switched on. The amount of mains electrical energy transferred is measured in kilowatt-hours, kWh. One unit is 1 kWh. E = P × t E is the energy transferred in kilowatt-hours, kWh P is the power in kilowatts, kW T is the time in hours, h. http://www.bbc.co.uk/schools/gcsebi...ergyefficiency/electricalappliancesrev1.shtml Does this neuter the claim in original post? "All calculation of energy requires the inclusion of a value for mass. If mass is unknown, energy cannot be calculated" Please Register or Log in to view the hidden image!