WiseCalcs

Electricity cost calculator

Enter the device's power in watts, how many hours it runs each day, and your price per kilowatt-hour. The calculator shows the daily, monthly, and yearly cost as you type.

Written by Kenneth Schrøder, Founder of WiseCalcs

Updated ·Sources verified

Daily cost = watts ÷ 1,000 × hours per day × price per kWh. See 30-day and yearly costs, then compare a second device at the same price.

W
h
USD

Monthly cost

$4.50

Daily cost
$0.15
Yearly cost
$54.75
Energy per year
182.5 kWh

Compare another device

Same price per kWh as above. Positive difference means B costs less.

Device A / year
$54.75
Device B / year
$109.50
Annual difference (A − B)
-$54.75

The result updates as you type. It shows the cost per day, per month, and per year, plus the energy the device uses over a year.

How does it work?

Watts are divided by 1,000 to get kilowatts. A month is 30 days and a year is 365 days. You supply the price per kWh from your bill.

Electricity cost formula

cost=W1000×h×price\text{cost} = \frac{W}{1000}\times h \times \text{price}
W
Power draw in watts.
h
Hours used per day.
price
Price per kilowatt-hour.

A 100 W device run 5 hours a day uses 0.5 kWh daily; at 0.30 per kWh that is 0.15 a day, about 4.50 a month and 54.75 a year.

Method & sources

Power is entered in watts and converted to kilowatts by dividing by 1,000. The device runs the same number of hours every day. A month is treated as 30 days and a year as 365 days.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

How we calculate

  • Power is entered in watts and converted to kilowatts by dividing by 1,000.
  • The device runs the same number of hours every day.
  • A month is treated as 30 days and a year as 365 days.
  • The price per kWh is the all-in rate you supply from your bill.
  • Fixed charges are excluded. Variable charges and taxes are included only if you include them in the entered kWh price. Standby must be entered as its own power and hours.

Rounding

Costs are rounded to two decimals and energy to one decimal for display. The calculation uses full precision.

Compare two appliances at the same electricity price

Enter device A above, then device B's watts and daily hours in the comparison. Both use your price per kWh. The annual difference is A minus B: a positive amount means B costs less to run. Purchase price and replacement costs are not included, so this difference alone does not establish whether buying a new device pays off.

Where to find your electricity price

Use the unit rate on your supplier's bill or tariff sheet. If the rate is in cents, divide by 100 before entering it. Include per-kWh charges and taxes you want represented in the result; fixed standing charges are separate. For a variable tariff, enter a representative rate for the hours you actually use the device. There is no automatic price lookup. The displayed currency follows the page language; no currency conversion takes place.

Three examples you can adapt

Illustrative inputs, not measured appliance averages: a 10 W lamp used for 5 hours needs 0.05 kWh/day; a 100 W device used for 3 hours needs 0.3 kWh/day; a 2,000 W heater running at full power for 2 hours needs 4 kWh/day. Multiply each by your unit rate. Use measured average power for devices that cycle on and off rather than assuming their maximum wattage runs continuously.

What this calculator does

Electricity is billed per kilowatt-hour (kWh) — running one kilowatt for one hour. This calculator turns an appliance's wattage and daily run time into kilowatt-hours, multiplies by your price, and shows what it costs over a day, a month, and a year.

How to use it

  1. Enter the device's power in watts (check the label or specifications).
  2. Enter how many hours it runs per day.
  3. Enter your price per kWh from your electricity bill.
  4. Read the daily, monthly, and yearly cost below.

A worked example

A 100 W device run 5 hours a day uses 0.5 kWh daily. At 0.30 per kWh that is 0.15 a day — about 4.50 a month and 54.75 a year, using around 182.5 kWh over the year.

Finding the wattage and price

Use the wattage on the device label or in its manual, or measure its average power. Find the price per kWh on your bill and include the variable charges you want represented in the result.

Common mistakes

  • Entering kilowatts in the watts field. A 2 kW heater is 2,000 W.
  • Using more than 24 hours a day. The field is capped at 24.
  • Forgetting that standby power and standing charges are not included.

When it's useful

Comparing the running cost of appliances, deciding whether an upgrade pays off, or checking what an always-on device adds to your bill.

FAQ

How is the cost calculated?
Watts are divided by 1,000 to get kilowatts, multiplied by the hours per day to get kWh, then multiplied by your price per kWh for the daily cost. Monthly and yearly figures use 30 and 365 days.
Where do I find the price per kWh?
It is on your electricity bill, usually as a unit rate. Use the all-in rate including any per-kWh charges for the most accurate result.
Does this include standing charges?
Fixed daily standing charges are not included. Variable taxes or charges are included only if they are part of the price per kWh you enter.
How do I convert amps to watts?
Use the device's rated watts or a measured power value. Amps times volts alone is not a reliable wattage estimate for every AC appliance because power factor can matter.
Which currency does it use?
The currency follows the site language. The energy math is identical in every market.
Can I share a calculation?
Yes. Use Share to copy a link that reopens the calculator with the same power, hours, and price.

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