Energy (kWh) = watts ÷ 1,000 × hours. Heaters, dryers and kettles use a lot of power but often run for a short time; fridges run all day.
FAQ
How much does a 1,000 W appliance cost to run 3 hours a day?
With the default numbers above – Cost for the period: $12.60.
Standard financial formulas (monthly compounding). Change any input to match your situation.