1. Calculate the power in watts of electricity it uses. (If the label gives only the number of amps and not the number of watts, then just multiply the amps by 120 to get the number of watts. (Amps x Volts = Watts, and most U.S. electricity is ~120 volts. So a hot plate rated at 6 amps uses 6 x 120 = 720 watts, on the highest setting.) Note that if a device is powered by a transformer (one of those great big plugs), then the transformer has converted the electricity from AC to DC, so you need to multiply by the DC voltage, not the AC voltage of 120. For example, if the device says "INPUT 9V, 0.5A", then that's 9 volts x 0.5 amps = 4.5 watts.
2. Estimate how much time the appliance is used in a typical 24 hour day. Convert that time to seconds. (For instance, if a fan is used 8 hours/day X (3600seconds/hour) = 28,800seconds)
3. You pay for the electricity supplied to you by the electric company based on the amount of energy you use. An electric meter keeps track of the total energy used by montoring the power (rate of energy use) and the amount of time each power level is maintained. Recall the equation for power is P=E/t, therefore E=Pt (i.e., the energy used is equal to the power times the time elapsed). Multiply the power calculated in step 1 by the time in secondsestimated in step 2 to determine the amount of energy (in Joules) used by the appliance in a typical day.
4. Since we pay for electricity based upon how many kilowatt hours we use you must convert Joules to kWh by deviding the number of joules calculated in step 3 by 3,600,000. 5. For this exercise assume that we pay 10 cents per kWh. Multiply the number of kWh calculated in step 4 by .1 to obtain the average cost of your appliances energy consumption in a typical day.