Electricity Cost Calculator
Enter the power of a device in watts, how many hours a day you use it and your price per kilowatt hour. We show what it costs.
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The formula
Energy (kWh) = watts x hours / 1000. Cost = kWh x price per kWh.
How it works
Power in watts tells you how fast a device uses energy. Multiply by the hours used and divide by 1,000 to get kilowatt hours (kWh), which is what your bill charges for. A 1,500 watt heater run for 4 hours uses 6 kWh.
An example
A 100 watt TV used 5 hours a day is 0.5 kWh a day, or 15 kWh a month. At 0.20 per kWh that is 3 a month and about 36.50 a year.
Where to find the wattage
Look at the label on the device or its power supply. If it only lists amps and volts, multiply them together to get watts. For anything with a motor or heating cycle, such as a fridge, the real average is lower than the label because it does not run constantly.
Biggest users in most homes
- Heating and cooling
- Water heating
- Cooking and tumble dryers
- Fridges and freezers, because they run around the clock
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Device power (watts): 100; Hours used per day: 5; Electricity price (per kWh): 0.2; Number of devices: 1 | Cost per month (30 days): $3.00 |
| Device power (watts): 1500; Hours used per day: 4; Electricity price (per kWh): 0.15; Number of devices: 1 | Cost per month (30 days): $27.00 |
| Device power (watts): 60; Hours used per day: 10; Electricity price (per kWh): 0.18; Number of devices: 4 | Cost per month (30 days): $12.96 |
Electricity Cost Calculator: frequently asked questions
What is a kWh?
A kilowatt hour is the energy used by a 1,000 watt device running for one hour. It is the unit on your electricity bill.
Where do I find my price per kWh?
On your electricity bill or tariff. Use the unit rate, and add the standing charge separately if you want the full cost.
How accurate is this estimate?
It is as accurate as the numbers you give it. Real-world amounts such as paint, concrete or fuel vary, so allow a margin.
Is what I enter in this tool saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this tool free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026