In order to calculate the average operating cost for any electrical appliance you can use the following formula:

watts/1000 = kW x hours of operation = kWh x kWh rate = cost

Watts can usually be found on the appliance nameplate. If the nameplate lists amps:

volts x amps = watts

Example:  How much does it cost to operate my portable electric heater? An electric heater wattage is usually given on the unit itself, or with the literature that comes with it.  Our example is 1000 watts. I use the heater an average of 45 hours during winter months (1/2 hour per day for the three winter months). The City of Ames (Iowa) Electric Services electric rate during the winter is $.068.  So -

1000 watts/1000 = 1 kW x 45 hours of operation = 45 kWh x $.068 = $3.06

Now we have an 8 amp heater. The calculation changes just a bit:

8 amps x 120 volts household current = 960 watts/1000 = .96 kW x 45 hours = 43.2 kWh x $.068 = $2.94