By understanding your energy usage, you can take charge of your electric bill. Use these formulas to help calculate your energy usage and projected costs.
A watt (W) is a measurement of power. Most appliances and light bulbs are labeled with the wattages they use.
A kilowatt (kW) is equivalent to 1000 watts.
A kilowatt-hour (kWh) is a measurement of energy consumption. It is the amount of power used over time, and the basis for how electric bills are calculated.
Calculate Energy Consumption: Power × Time = Energy. For example, using a 100-watt bulb for 10 hours equals 1 kWh. (100 watts × 10 hours = 1000 watt-hours or one kilowatt-hour.)
Calculate Energy Costs: Power (kW) × Time (hours of operation) × Price ($/kWh) = Cost of Operation
To find out how much it may cost to run a specific appliance, follow these 5 easy steps. Keep in mind that you are billed per kilowatt-hour (kWh), or for how much electricity you use in one hour. Examples are based on an average cost of $0.144 per kWh.
- Obtain the wattage (watts) from the appliance nameplate. Example: A quartz heater with a nameplate of 1500W. Note: if listed as kW, skip to step 3. If amps are specified, multiply amps × voltage to obtain watts.
- Divide the number of watts by 1000 to get kW. Example: 1500W ÷ 1000 = 1.5kW.
- To find out how many kilowatt-hours (kWh) the appliance uses, multiply the kW × the number of hours* the appliance is running each day. Example: The heater runs for 10 hours per day = 1.5kW × 10 hours = 15 kWh per day.
*If the appliance operates for less than one full hour, (i.e. a hair dryer), divide the number of minutes by 60. For example, a hair dryer is used 5 minutes each day, or 5 ÷ 60 = 0.083 hours per day. A 1250W hair dryer = 1.25kW × 0.083 hours per day = 0.1 kWh per day.
- To calculate the daily operating cost, multiply the kWh of the appliance by the average cost per kWh. Example: The quartz heater daily cost = 15 kWh × $0.144 = $2.16 per day to operate.
- To calculate the monthly operating cost, multiply the daily cost by the number of days the appliance is used during the month. Example: If you run the 1500W quartz heater 10 hours per day, 30 days per month = 15 kWh × $0.144 × 30 = $64.80.
Remember: Calculate and Conserve! For the example used, you might want to conserve energy by putting the heater on a thermostat or timer to decrease the time it is used.