Calculating What an Appliance Actually Costs to Run, With a Worked Example
Converting an appliance's wattage to kilowatts, multiplying by hours of daily use to get kilowatt-hours per day, and then multiplying by the local electricity rate per kilowatt-hour gives the actual daily cost — extending that daily figure to a month or year gives a concrete, comparable cost figure for any specific appliance.
This calculation turns an abstract wattage number (printed on most appliances) into a concrete, comparable dollar figure that actually means something for a household budget.
A worked example
A 1,500-watt space heater used 5 hours a day: 1,500 watts = 1.5 kilowatts. 1.5 kW × 5 hours = 7.5 kilowatt-hours per day. At an electricity rate of $0.15 per kilowatt-hour, that's 7.5 × $0.15 = $1.125 per day, or roughly $33.75 for a 30-day month of that usage pattern.
Why wattage alone doesn't tell the full cost story
A high-wattage appliance used briefly can cost less overall than a lower-wattage appliance left running continuously — the actual cost depends on both wattage and total hours of use, which is exactly why the full calculation (not wattage alone) is needed to compare the real cost of running different appliances.
Using this to identify the biggest cost contributors
Running this calculation for each major appliance in a household — particularly ones used for extended hours, like heating, cooling, or a water heater — reveals which specific appliances actually drive the most electricity cost, information a total monthly electric bill alone doesn't break down.