Electricity cost calculator
Enter an appliance's power in watts, the hours it runs and your rate in cents per kWh. You get the energy used and the cost per day, month and year.
Free · no signup Runs in your browser
How do I work out what an appliance costs to run?
Multiply the power in watts by the hours of use and divide by 1,000 to get kilowatt-hours (kWh), then multiply by your rate. A 1,500 W space heater running 3 hours a day uses 1,500 × 3 ÷ 1,000 = 4.5 kWh a day. At 12.5 cents per kWh that is 56 cents a day, about $17 a month. Your rate is on your electricity bill; because bills can include tiers and delivery charges, the true cost per kWh may be higher.
Why we built this calculator
Most people have no idea what an appliance really costs to run. A space heater, a second fridge, a gaming PC, an electric kettle and a dehumidifier all use power, and the bill is the sum of them. Looking at the energy used by each makes the biggest users obvious and shows whether a change, such as turning something off at the wall or buying a more efficient model, is worth it. This calculator does the arithmetic for up to six appliances at once, using your own rate.
Everything is worked out in your browser. Nothing you enter is sent anywhere.
How it works
Power is measured in watts, and energy is power used over time. A kilowatt-hour (kWh) is the energy used by a 1,000-watt appliance running for one hour, and it is what electricity is billed in. For each appliance the tool works out kWh per day as watts × hours × number of units ÷ 1,000. Multiplying by your rate, which you enter in cents per kWh and the tool divides by 100, gives the cost per day; a month is taken as 30.44 days (365 ÷ 12) and a year as 365 days. The total of all the appliances is shown with the energy per year. You can add a fixed monthly charge, such as a service fee on your bill, to see the all-in monthly amount. Watts are on the appliance's label or in its manual; a plug-in power meter gives the real use.
How to use it
- Find your rate on your electricity bill, in cents per kWh, and enter it.
- For each appliance, enter its name, power in watts, the hours it runs on a typical day and how many you have.
- Read the cost per day, month and year, and the energy each uses.
- To compare, change the hours or replace the appliance's watts with a more efficient model's.
- For appliances that cycle on and off, such as a fridge, use the average hours of running or measure the use with a power meter.
Use cases
- Finding which appliances cost the most to run
- Checking the cost of a space heater, air conditioner or dehumidifier
- Working out the payback on a more efficient appliance
- Comparing leaving a device on standby with switching it off
- Budgeting for a home office or a gaming PC
- Splitting the electricity cost of a shared appliance
Problems you may run into
Most surprises come from the rate and from appliances that cycle.
| What you see | Likely cause | What to do |
|---|---|---|
| My bill is higher than the total | Bills include delivery, tiers or time-of-use prices and taxes on top of the energy rate | Use your all-in cost per kWh (bill total ÷ kWh used), or add the fixed charge |
| I do not know my appliance's watts | It is on the rating label, or the label gives volts and amps | Watts = volts × amps; or use a plug-in power meter for the real figure |
| A fridge or heater cycles on and off | It does not run the whole time | Enter the average hours it is actually running |
| Cents or dollars | The rate is in cents per kWh | A rate of 12.5 means 12.5 cents, not 12.5 dollars |
| Heating and cooling | Their use changes with the weather | Run it for the heavy months and the light months separately |
| The numbers look small | Many appliances use little on their own | Look at the total and at standby power, which adds up across many devices |
Cutting the cost
The biggest users are usually heating and cooling, water heating, the clothes dryer, the oven and anything that runs all day. Lowering the hours, using the right setting, sealing drafts and replacing very old appliances with efficient ones all reduce the kWh. Some utilities charge less at off-peak times, so moving use to those hours can lower the bill without using less. Check your own utility's rates and programs.
The formula
How the answer is worked out.
kWh per day = watts × hours a day × number of units ÷ 1,000cost per day = kWh per day × rate in dollars per kWh (rate in cents ÷ 100)a month = 30.4375 days; a year = 365 daysyour all-in cost per kWh = the bill total ÷ the kWh used
The rate is the one you enter. Real bills can have tiers, time-of-use prices, delivery, and other charges. Hours are an average per day.
Example: a 1,500 W heater, 3 hours a day
Rate 12.5 cents per kWh.
- Energy per day1,500 × 3 ÷ 1,000 = 4.5 kWh
- Cost per day4.5 × $0.125 = $0.5625
- Month4.5 × 30.44 = 137 kWh, $17.12
- Year1,642.5 kWh, $205.31
About $17 a month
Running the heater for 6 hours would double it.
Terms on this page
- kWh
- Kilowatt-hour: the energy used by 1,000 watts in one hour.
- Standby power
- Power a device uses when it is off but plugged in.
Common questions
How do I calculate the cost of running an appliance?
Watts × hours ÷ 1,000 gives kWh, and kWh × your rate gives the cost.
What is a kWh?
The energy used by a 1,000 W appliance in one hour.
Where do I find my rate?
On your electricity bill, in cents per kWh.
How do I find an appliance's watts?
On its label or in the manual, or measure it with a plug-in power meter.
Does it include delivery charges?
Only if you enter your all-in rate.
Is anything I enter sent to a server?
No. The calculation happens in your browser and nothing you type leaves your device.
Where these numbers come from
- Wikipedia — Kilowatt-hour What a kWh is and how electricity is billed.
- Wikipedia — Watt The unit of power.
Last verified 2026-10-25 The method on this page is checked against the sources above at least once a year. Spotted something out of date? Tell us and we will fix it.
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