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Electricity Cost Calculator for Appliances
Enter an appliance's power in watts, how long it runs and what you pay per kilowatt-hour. The calculator shows the energy used and the running cost per day, week, month and year, with optional duty cycle and carbon figures.
Power, energy and cost
Power is the rate of using energy, measured in watts. Energy is power used over time, and bills charge for energy in kilowatt-hours (kWh). One kWh is one kilowatt (1,000 watts) running for one hour.
kWh = watts ÷ 1000 × hours
Cost = kWh × price per kWh
A 1,500 W heater used for 4 hours consumes 1.5 × 4 = 6 kWh a day. At 0.15 per kWh that is 0.90 a day, 27.38 for an average month and 328.50 a year. A 100 W device left on for 24 hours uses 2.4 kWh, which at 0.20 per kWh costs 0.48 a day.
Annual energy is the weekly total multiplied by 365 ÷ 7, and the monthly figure is one twelfth of that, so months of different lengths are averaged.
Rated power versus real consumption
The wattage printed on an appliance is usually its maximum or nameplate rating. Many devices rarely run at that level for the whole time. A thermostat-controlled heater, a refrigerator or an air conditioner switches its heating element or compressor on and off, so its average draw is a fraction of the rating. The duty cycle field applies that fraction. If a fridge rated at 150 W runs its compressor about 40% of the time, enter 40.
For the most accurate figure, use a plug-in energy monitor and read the kWh over a few days, then compare it with the estimate. Devices with motors may draw more briefly when starting, and standby power from electronics adds a small continuous load that is easy to forget.
Getting the price per kWh right
Use the unit rate from your own bill, and check whether it already includes taxes. Many tariffs are not a single flat rate: some charge more for the first block of usage, some charge different rates by time of day, and many add a daily standing charge regardless of use. This calculator multiplies energy by one rate, so the result is a good estimate of the marginal cost of running one appliance, not the whole bill. If your tariff varies by time of day, calculate the peak and off-peak hours separately and add them.
Solar owners and people with a battery should use the value of the energy at the time of use, which can differ from the grid price.
Limits
The calculator treats power as constant while the appliance is on. It covers resistive loads and typical household appliances well, but it ignores power factor, three-phase supply and demand charges that matter to commercial users. For circuit sizing, wiring and safety, rely on a qualified electrician and local rules, not on this estimate. To work out the electrical quantities behind a rating, see the watts, amps and volts calculator.
Worked example
A 1,500 W electric heater runs 4 hours every day. Electricity costs 0.15 per kWh on the bill.
Inputs
| Appliance power | 1500 |
|---|---|
| Power unit | Watts (W) |
| Hours used per day | 4 |
| Days used per week | 7 |
| Share of the time it draws full power | 100 % |
| Number of identical appliances | 1 |
| Electricity price per kWh | 0.15 |
Result
328.50 per year for 2,190 kWh.
| Energy per hour of use | 1.500 kWh |
|---|---|
| Energy per day of use | 6.000 kWh |
| Energy per week | 42.00 kWh |
| Energy per month (average) | 182.50 kWh |
| Energy per year | 2,190.0 kWh |
| Cost per hour of use | 0.2250 |
| Cost per day of use | 0.90 |
| Cost per week | 6.30 |
| Cost per month (average) | 27.38 |
| Cost per year | 328.50 |
- Cost is energy only. Standing charges, taxes, tiered or time-of-use tariffs and demand charges are not included.
Accuracy note: Results are calculated in your browser from the values you enter. Check anything that matters for legal, academic or financial purposes against the official source.
Frequently asked questions
How do I calculate the cost of running an appliance?
Divide the power in watts by 1,000, multiply by the hours of use to get kilowatt-hours, then multiply by your price per kWh. The calculator then scales it to week, month and year.
What is a kilowatt-hour?
A kilowatt-hour is the energy used by a 1,000-watt device running for one hour. It is the unit most electricity bills use to charge for consumption.
Why is my real usage lower than the rated wattage suggests?
Many appliances cycle on and off under thermostat control, so they draw full power only part of the time. Enter that share in the duty cycle field to match.
Does this include standing charges and taxes?
No. It multiplies energy by the single price you enter. If your price already includes taxes, they are covered, but fixed daily charges are not part of the estimate.
Can I use it for several appliances at once?
Run it once per appliance and add the monthly costs. For identical devices, set the quantity field to the number you have.