Electricity cost depends on power, time, and the rate charged per kilowatt-hour. The label on an appliance is a useful starting point, but real usage may cycle on and off.
The conversion
Divide watts by 1,000 to get kilowatts, then multiply by hours used to get kilowatt-hours. Multiply that energy by the electricity rate for the cost estimate.
A simple example
A 1,000-watt heater used for two hours consumes about 2 kWh. At $0.20 per kWh, that session costs about $0.40 before taxes or other bill components.
Account for cycling and tiers
Refrigerators, air conditioners, and thermostatic devices may not draw rated power continuously. Time-of-use pricing, delivery charges, taxes, and tiered rates can also change the final bill.
A worked example
Worked example: a 1,500-watt heater used for two hours consumes about 3 kWh. At $0.20 per kWh, the energy charge is about $0.60 before fixed fees and taxes.
Check whether the appliance cycles rather than drawing its rated power continuously. Use the rate from the actual bill, including time-of-use or tiered pricing when relevant.
For a whole bill, repeat the estimate for the largest appliances and add always-on loads. The appliance label may show maximum power, so a plug meter can improve the estimate for cycling devices.
Use the calculator for comparisons and trend estimates, but use the utility bill's effective rate when budgeting the household total.
Use the estimate to compare habits and appliances, then reconcile it with the rate structure on the actual bill.
COMMON QUESTIONS
Frequently asked questions
Is a watt the same as a kilowatt-hour?
No. A watt measures power; a kilowatt-hour measures energy used over time.
Why is my bill higher than the appliance estimate?
The estimate may omit other appliances, cycling patterns, delivery fees, taxes, and rate tiers.