To estimate an appliance's electricity cost, divide its average power in watts by 1,000, multiply by the hours it runs, then multiply by your price per kilowatt-hour. The result is the variable energy cost for that period. Fixed utility charges are separate.
Use the electricity cost calculator to compare two usage patterns. This guide explains which numbers to enter and how to interpret the difference.
Watts and kilowatt-hours are different
Watts measure power at a moment in time. Kilowatt-hours measure energy over time. A 1,000-watt appliance operating continuously for one hour uses 1 kWh. A 100-watt appliance operating for ten hours also uses 1 kWh. The U.S. Energy Information Administration explains these units.
The distinction matters because a high-power device used briefly can consume less energy than a lower-power device left on all day.
A worked running-cost example
Suppose an appliance averages 1,500 watts, runs two hours per day, and electricity costs 0.20 per kWh in your currency. These are illustrative inputs, not a local tariff or an appliance recommendation.
| Step | Calculation | Result |
|---|---|---|
| Convert power | 1,500 ÷ 1,000 | 1.5 kW |
| Daily energy | 1.5 × 2 hours | 3 kWh |
| Daily cost | 3 × 0.20 | 0.60 |
| 30-day cost | 0.60 × 30 | 18.00 |
| 365-day cost | 0.60 × 365 | 219.00 |
At one hour per day, the annual cost falls to 109.50. The difference is 109.50 per year if the same usage pattern and tariff persist. If a replacement appliance costs 300 to achieve that saving, the purchase price still needs to be considered; the saving alone does not make replacement worthwhile.
Find the right electricity rate
Use the energy charge from your bill or tariff in currency units per kWh. Enter 0.20 for 20 cents, not 20. Keep fixed daily or monthly charges separate when asking how much one appliance adds to a bill.
If prices differ by time of day, split the calculation into peak and off-peak periods and add the results. An average rate can give an initial estimate, but it hides the value of shifting usage. Check whether the rate includes applicable taxes and variable delivery charges.
Use measured consumption when possible
An appliance's maximum power rating is not necessarily its average draw. Thermostatically controlled devices may cycle on and off, while variable-speed equipment changes power with conditions. Heating also depends on weather and settings.
If an energy label or monitor gives actual kWh over a representative period, multiply those kWh directly by the applicable rate. There is no need to reconstruct energy from maximum wattage. For a heat pump, distinguish electrical input from heat output; see how heat pumps work.
Why the estimate differs from a bill
The calculator assumes the same daily use for each day. Actual weather, occupancy, billing days, and tariffs vary. It calculates one load, while your bill combines many loads and other charges. A difference between the estimate and your total bill is not itself evidence of a billing error.
Compare like periods and record the assumptions. For a large purchase, obtain equipment-specific estimates. Start by comparing the same appliance at two running times, then compare a replacement's measured consumption for the same useful output. Use the solar payback calculator when comparing generation with buying electricity from the grid.