Electricity Cost Calculator
What one appliance costs to run: watts, hours, kilowatt hours and the price of each one.
An appliance label gives you watts, and the bill gives you kilowatt hours. The distance between the two is the only arithmetic you need to know which appliance is actually expensive to run.
Enter the power, how many hours a day it runs and your price per kilowatt hour, and this calculator shows the energy used and what it costs per day, per month and per year.
At a glance
- What you enter
- Power rating, Hours used per day, Days used per month, Price per kWh, How many of them
- What you get
- Cost per month, Cost per year, Cost per day, Cost per hour of use
- Formula shown
- Yes - every step, right below your results.
- Cost and privacy
- Free, no account needed, and nothing you type is stored.
See worked examples ↓ Read the FAQ ↓ Share this calculator ↓
Results are estimates for general information only - always verify with a professional or official source before acting on them.
How to use the Electricity Cost Calculator
- 1 Enter Power rating (watts)
- 2 Enter Hours used per day (hours)
- 3 Enter Days used per month (days)
- 4 Enter Price per kWh
- 5 Enter How many of them
- 6 Press Calculate. You get Cost per month, Cost per year, Cost per day, Cost per hour of use, and every intermediate step stays visible under “How is this calculated?”
- 7 Change one number at a time to see what moves the result - that is usually the most useful thing a calculator can tell you.
Worked examples
Real numbers run through this calculator. Open any example to load it into the form above and change it.
Eight 50 watt halogen downlights left on four hours a day
Lighting that is cheap per bulb but adds up across a room at 30 cents per kWh.
You enter
- Power rating
- 50 watts
- Hours used per day
- 4 hours
- Days used per month
- 30 days
- Price per kWh
- $0.30
- How many of them
- 8
You get
- Cost per month
- $14.40
- Cost per year
- $172.80
- Cost per day
- $0.48
- Cost per hour of use
- $0.12
The eight lights use 1.6 kWh a day, which costs $0.48. Over a month of 30 days that is 48 kWh and $14.40, and over a year $172.80 for 576 kWh. One hour with all eight running costs $0.12. Replacing them with 9 watt LEDs would cut the power by more than four fifths, and the same hours would cost about $31 a year at this price.
A 2,500 watt tumble dryer used on twelve days a month
A high-power appliance used often enough to cost more per year than the lighting.
You enter
- Power rating
- 2,500 watts
- Hours used per day
- 2 hours
- Days used per month
- 12 days
- Price per kWh
- $0.30
- How many of them
- 1
You get
- Cost per month
- $18.00
- Cost per year
- $216.00
- Cost per day
- $1.50
- Cost per hour of use
- $0.75
Two hours of drying uses 5 kWh a day, which costs $1.50. On twelve days a month that is 60 kWh and $18.00, and the year works out at $216.00 for 720 kWh, more than the eight lights cost even though it runs on only 144 days. One hour of drying costs $0.75, so halving the time per load would take about $108 off the annual figure.
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Frequently asked questions
Where do I find my price per kilowatt hour?
On the bill, usually as a rate per kilowatt hour plus a standing charge. If the bill only shows a total, divide the amount charged for energy by the kilowatt hours used in the same period. A $96 charge for 320 kWh is 30 cents per kWh.
Add the standing charge into the rate if you want the full cost of running the appliance, or leave it out and treat it as a fixed cost you pay whatever you use. Either is defensible as long as you are consistent when comparing two tariffs.
Is the yearly figure based on 365 days?
No. The monthly cost is the daily cost multiplied by the days per month you enter, and the yearly cost is the monthly figure multiplied by twelve. With 30 days entered, the year is counted as 360 days, so the annual figure is a little below a true 365-day year.
That matters most for something used every day. For a precise annual figure you can enter 30.4 days, or simply add about 1.4% to the result. For an appliance used on twelve days a month, the annual figure assumes those twelve days happen in every month.
Why is my real consumption different from the label?
The calculation assumes the appliance draws its rated power the whole time it is switched on. A fridge cycles, a washing machine heats for part of its cycle, a laptop charges and then draws very little, and a device on standby uses a fraction of its rating. Heating and cooling appliances use more or less depending on the room and the weather.
For anything that runs constantly, a plug-in energy monitor gives a much better figure than the label. For everything else the estimate is accurate enough to rank appliances against each other, which is the decision it is there to inform.
How do I compare two appliances fairly?
Compare the cost per hour first, then multiply by the hours each one really runs. A 2,000 watt heater costs more per hour than a 50 watt light, but a light left on for six hours can cost more in a day than the heater run for ten minutes.
The annual cost is the fairest single number because it contains both, as long as you enter realistic hours and days for each appliance. When one appliance replaces another, compare the two annual figures rather than the two power ratings.