I want to calculate the total energy consumed by my lan switch in one month. It has a AC adapter with rating--> Input = 100-240V ~ 0.6A Output = 5V - 1500 mA Note:First I will calculate in joules then convert it in kWh. At first, i was considering calculating using the input rating so the formula goes, E = I2Rt E = IVt .....as V=IR I = 0.6A V=240V(230-240V in India) t = 60 x 60 x 24 x 30 (for a month ) Therefore, E = 240 x 0.6 x 60 x 60 x 24 x 30 E = 124416000 J E = 103.68 kWh And this is not possible as it is too much. It will cost me around Rs.777.6 and by total bill is Rs.3000. How is it possible? Should I take the output rating or i am correct?