Use your own tariff and a useful measurement
An appliance's running cost depends on how much energy it uses and the price you pay for that energy. Watts describe power at a moment; kilowatt-hours, or kWh, describe energy used over time. A high-power appliance used briefly may consume less energy than a lower-power device left running for days.
Use the usage rate from your electricity plan, expressed in dollars per kWh. For example, 30 cents is $0.30. The daily supply charge is separate and usually does not disappear when you switch off a device. The examples below are arithmetic illustrations, not typical appliance measurements or a quoted electricity price.
A running-cost worksheet
For a device drawing steady power, use:
Energy in kWh = watts ÷ 1,000 × hours used.
Cost in dollars = kWh × your applicable dollars-per-kWh tariff.
Write down the device, the source of its power figure, hours used and tariff. If your meter gives total kWh for the period, use that reading directly and skip the watts calculation.
Worked example A: a hypothetical 60-watt device running for 5 hours uses 60 ÷ 1,000 × 5 = 0.30 kWh. At an illustrative $0.30/kWh, that costs $0.09.
Worked example B: a hypothetical steady 2,000-watt load used for 15 minutes uses 2,000 ÷ 1,000 × 0.25 = 0.50 kWh, costing $0.15 at the same example rate.
Worked example C: a meter records 4 kWh over a week. At an illustrative $0.30/kWh, that week's usage costs $1.20. Substitute your actual rate rather than treating these prices as a forecast.
Allow for cycling and changing power
A refrigerator compressor cycles, a washing machine changes tasks during a program, and an inverter air conditioner adjusts its output. Multiplying the maximum rated input by every hour the device is connected can overstate normal consumption. A heating or cooling capacity figure is also not necessarily electrical input power.
For a compatible plug-in device, an appropriately rated energy meter can measure a representative period. Include normal cycles and standby time. Follow the meter and appliance instructions; do not use a plug-in meter on hardwired equipment or beyond its rating. Ask a qualified professional when measurement would require electrical work.
If you only have an assumed duty cycle, label it as an assumption: energy = input kW × hours × fraction of time drawing that input. This is a rough model and does not capture every changing load. Replacing the assumption with measured kWh usually gives a more useful estimate.
Compare similar appliances using their labels
For products with an Energy Rating Label, compare models of similar size and capability. The consumption figure comes from standard test assumptions; your climate, settings and usage can differ. Energy Rating explains the label and annual-cost calculation. Its official calculator helps compare supported appliance models.
For illustration, 300 kWh per year multiplied by $0.30/kWh equals $90 per year under those assumptions. Do not add that annual figure to a separate watts estimate for the same appliance: they are alternative ways of estimating its consumption. Our home-office guide discusses printers, whose specifications need a different comparison from household star labels.
Handle tariffs and solar carefully
For time-of-use pricing, split measured use between the applicable periods and multiply each amount by its rate. Demand charges and controlled-load arrangements need their own treatment. Check the plan rather than applying a single headline price to every hour.
Energy used while solar is generating may change what you import or export. Treat any forgone feed-in payment separately from grid usage and avoid assuming all daytime electricity is free. This worksheet estimates a device's usage cost; it does not reproduce an entire electricity bill.
Use the result to compare sensible operating changes, then check real bills or measurements. Before replacing equipment, consider purchase and installation costs, repair options and official assistance.
About this guide
Prepared with AI assistance using the sources linked in this guide. Sources checked on 14 October 2026. This is original Simply Maid guidance, not a republication of the former My Green Life website.
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