Device Electricity Cost Calculator
By Mustafa Bilgic · Updated 21 August 2026
The electricity cost of any device equals its wattage multiplied by its running hours, divided by 1,000, then multiplied by your electricity rate per kWh. Enter three numbers into the calculator above and it returns your daily, monthly and yearly cost in seconds. No sign-up, no stored data.
This calculator runs entirely in your browser and stores nothing. Tudug is reader-supported; ads help keep the tools free.
The kWh formula behind every electricity bill
Every electricity bill rests on one calculation: watts x hours / 1,000 x price per kWh. Watts measure how hard a device pulls power at any moment. Running it for a set number of hours gives you watt-hours. Dividing by 1,000 converts that to kilowatt-hours, which is what your supplier charges for.
A 2,000 W space heater left on for 5 hours uses 10 kWh. If your tariff is $0.15/kWh, that session costs $1.50. A 10 W LED lamp running the same 5 hours uses 0.05 kWh and costs less than a cent. The formula is identical both times; only the wattage changes the outcome dramatically.
Your kWh rate varies by country, state, supplier and time of day. This tool lets you type your own rate so the result matches your actual bill rather than some average that may be half or double what you pay.
Where to find watts and kWh price
The wattage of most appliances is printed on a label on the back or bottom of the device. Laptops and phone chargers list it on the power brick. If you see amps instead of watts, multiply amps by your mains voltage (120 V in North America, 230 V in most of Europe and the UK) to get an approximate wattage.
Your kWh price appears on your electricity bill or your supplier's tariff page. Look for the line labelled unit rate or energy charge. Some plans have a flat rate; others charge more during peak hours. If you have a time-of-use tariff, enter the rate for the period when the device actually runs.
Devices with variable loads — air conditioners, fridges, gaming PCs — cycle on and off or ramp up and down. For these, the rated wattage is the maximum draw. Real consumption over a full day is usually 40-60% of the label figure. A plug-in power meter gives the truest reading.
Common devices ranked by running cost
Electric heaters and air conditioners sit at the top because they pull 1,000-3,000 W for hours at a stretch. A single portable heater on 8 hours a day can add $30-$50 per month at typical North American rates. Central air conditioning in summer easily doubles or triples that.
Kitchen appliances are power-hungry but run briefly. An oven at 2,400 W for one hour costs roughly the same as a 60 W desk fan running all day. Duration matters as much as wattage.
Electronics that stay on 24/7 — routers, NAS boxes, standby-mode TVs — draw little per hour but never stop. A 15 W router running all year uses about 131 kWh. Individually small, these background loads stack up across an entire house. Plug each one into the calculator above to see the cumulative yearly bill.
Three ways to cut device electricity costs
Reduce hours. The simplest lever. A smart plug or timer that turns off a space heater after 3 hours instead of 8 cuts its cost by more than half, with the same formula and same wattage.
Reduce watts. Swapping a 60 W incandescent bulb for a 9 W LED cuts lighting cost by 85%, with identical brightness. The same logic applies to replacing an old desktop PC (200-350 W at idle) with a modern laptop (30-60 W under load).
Shift to cheaper hours. If your supplier offers a time-of-use tariff, running high-draw appliances — dishwashers, tumble dryers, EV chargers — during off-peak hours saves money without changing what you use or how long you use it. Check your bill for the off-peak window and set timers accordingly.
Frequently asked questions
How do I calculate electricity cost from watts?
Multiply the device's wattage by the number of hours you run it, divide by 1,000 to get kWh, then multiply by your electricity rate. A 100 W device running 10 hours at $0.12/kWh costs $0.12.
Why does the calculator ask for my own kWh rate?
Electricity prices vary enormously by region and plan. Plugging in a generic average would give you a number that might be half or double your real bill. Your actual unit rate keeps the result accurate.
Should I use the rated wattage or actual wattage?
The rated wattage on the label is the maximum the device can draw. For constant-draw devices like heaters, it is close enough. For variable-load appliances like fridges or gaming PCs, actual consumption is lower and a plug-in power meter gives a more accurate figure.
Does standby mode still cost money?
Yes, but usually very little. Most modern devices draw 0.5-3 W in standby. That adds up to a few dollars a year per device. If you have dozens of devices on standby, the total can become noticeable.