Appliance Energy Use Calculator (kWh)
Enter your appliance's power, how many hours a day and how many days a month you use it, and see the energy it draws in kWh — plus the cost, using the electricity price from your own bill
Appliance Details
You can find the watts on the appliance's rating label
Find it on your electricity bill, usually listed as the cost per kWh
How Appliance Energy Use Is Calculated
Electricity is billed in kilowatt-hours (kWh). One kWh is the energy used by a 1,000-watt device running for one hour. So the energy an appliance uses is its power in watts, multiplied by the hours it runs, divided by 1,000.
The formula: kWh per day = watts × quantity × hours per day ÷ 1,000. Monthly use multiplies that by the days you use it each month, and the yearly figure multiplies the monthly one by 12. Cost is simply kWh × the price per kWh you enter.
Estimated Consumption
Add your price per kWh to see what this appliance costs
How to use this tool
- Enter the appliance's power and pick W or kW; the watts are on its rating label.
- Set the hours per day, the days per month and the quantity of identical appliances.
- Optionally add your price per kWh (from your electricity bill) and a currency symbol to see the running cost.
- Read the energy per day, month and year, then copy the result.
Worked example
A 150 W appliance (say, a desktop computer) used 8 hours a day for 30 days draws 150 × 8 = 1,200 Wh, which is 1.20 kWh per day, 36.00 kWh per month and 432.00 kWh per year. At an illustrative price of $0.30 per kWh, that is about $10.80 a month, or $129.60 a year. Two identical units would simply double each figure. Note that the label shows peak power: a device that cycles on and off, like a fridge, uses less than watts × hours suggests, so lower the hours to the share of time it really runs.
Methodology
This calculator applies the SI definition of the watt — one joule of energy per second — and the standard billing unit of electricity, the kilowatt-hour: 1 kWh equals 1 kW sustained for one hour, or exactly 3.6 megajoules. Daily energy is computed as E (kWh) = P (W) × quantity × t (h) ÷ 1,000, scaled by the days of use per month and by 12 for the year. Standby draw, which the International Energy Agency's One Watt Initiative sought to limit, can be modeled by entering the idle power in watts and 24 hours per day.
Six example loads and what the tool does with them
These are example inputs, not typical figures for any product. Each row shows what the tool returns (kWh, two decimals):
| Input (power × qty × hours × days) | Per day | Per month | Per year |
|---|---|---|---|
| 60 W × 6 h × 30 days | 0.36 | 10.80 | 129.60 |
| 100 W × 4 h × 30 days | 0.40 | 12.00 | 144.00 |
| 1500 W × 0.5 h × 30 days | 0.75 | 22.50 | 270.00 |
| 2000 W × 1 h × 20 days | 2.00 | 40.00 | 480.00 |
| 1200 W × 2 h × 31 days | 2.40 | 74.40 | 876.00 |
| 10 W × 2 × 24 h × 30 days | 0.48 | 14.40 | 172.80 |
How to read it: the yearly figure is the daily energy times 12 × the days per month, capped at 365. With 30 days a month that is 360 days, which is why 0.36 kWh a day gives 129.60 a year, not 131.40. At 31 days the cap applies: 2.40 × 365 = 876.00. For cost, multiply a column by your own price per kWh.
The tool uses the power you type and assumes constant use. Appliances that cycle, like refrigerators, draw less than their label suggests, so use average watts from a plug-in meter where you can.
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Frequently Asked Questions
Where do I find my appliance's wattage? ▼
Look for the rating label on the back, bottom or door frame, or in the manual — it lists watts (W) or kilowatts (kW). If it only shows volts and amps, multiply them to get an approximate wattage. A plug-in energy meter gives the most accurate reading.
Why does my refrigerator use less than its label says? ▼
The label shows the power while the compressor is running, but a refrigerator's compressor only runs part of the time to hold its temperature. Enter the hours it really runs or, better, measure for 24 hours with a plug-in meter and enter the average watts (kWh × 1,000 ÷ 24).
Where do I find the price per kWh, and what if my rate changes? ▼
Check your electricity bill for the energy charge per kWh — it is often listed by tariff or tier. Enter the rate you pay, or an average if you have tiered or time-of-use pricing. This tool never presets a price, so it stays correct whenever your rate changes.
How much does standby power add up to? ▼
A device idling at 5 watts around the clock uses 5 × 24 ÷ 1,000 = 0.12 kWh per day, or 3.6 kWh in a 30-day month. Multiply by the number of idle devices in your home to see the total.