How to Calculate kWh

If you're concerned about saving energy, want to better understand your electric bill, or are just curious about how much power you're using, you need to figure out your kilowatt-hour, or kWh, consumption.

Instructions

  • Step 1: Study this example of a ceiling fan. The fan is 100 watts multiplied by 4 hours per day multiplied by 120 days per year and divided by 1000 equals 48 kilowatts. Multiply 48 by × 6.5 cents per kilowatt hour to arrive at $3.12 per year.
  • Step 2: Estimate the number of hours for a refrigerator by dividing the total time the refrigerator is plugged in by three. Although they're on all the time, they actually cycle on and off to maintain interior temperatures. With a little calculation, you should be able to figure out which of your appliances are the biggest drains on your electricity consumption.
  • FACT: In 2008, the average annual electricity consumption for a U.S. residence was 11,040 kilowatt hours. Tennessee had the highest annual consumption at 15,624 kilowatt hours and Maine the lowest at 6,252 kilowatt hours.
  • Step 3: Multiply this by the number of days per year the appliance is used to find the annual consumption. Then find the annual cost to run an appliance by multiplying the kilowatt per year by your local utility's rate per kilowatt consumed, which should be listed on your bill.
  • Step 4: Know the formula for calculating kilowatt consumption. Wattage times hours used per day divided by 1000 equals daily kilowatt-hour consumption.
  • Step 5: Find the wattage of the appliance, usually stamped on the bottom or back of the appliance. The wattage listed is the maximum power drawn by the appliance. Many appliances have a range of settings so the actual amount of power consumed depends on the setting used at any one time.
  • TIP: If the wattage is not listed on the appliance, estimate it by finding the current draw in amperes and multiplying that by the voltage used by the appliance.
  • Step 6: Understand that one kilowatt, abbreviated kW, is equal to 1,000 watts.

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