Most people guess wrong about where their electricity goes. They unplug phone chargers and leave a space heater running for hours. They worry about the TV and forget the tumble dryer. The fix isn't guilt or guesswork. It's one unit, one formula, and a few minutes with the calculator below.
A watt measures how fast something uses energy right now. A kilowatt-hour (kWh) is what you actually pay for: using 1,000 watts for one hour. A 1,000-watt microwave running for an hour uses 1 kWh. A 10-watt router running for 100 hours also uses 1 kWh. That's the whole trick: power times time.
For scale: the average US household bought about 10,791 kWh of electricity in 2022, about 899 kWh a month, according to the US Energy Information Administration. The average US residential price in August 2026 was 18.16 cents per kWh, so a month like that comes to roughly $163 at that average price. In the UK, the Centre for Sustainable Energy uses an average price of 26p per kWh as of July 2026.
| Usage (kWh) | How much electricity you used in the billing period, from your meter. This is the number you can change. |
| Unit rate | The price per kWh. Some tariffs charge different rates at different times of day. |
| Fixed / standing charge | A daily or monthly amount you pay just for being connected, however little you use. |
| Estimated vs. actual | If the reading is marked "estimated," the company guessed. Submitting a real meter reading can fix a bill that's too high (or too low, which catches up with you later). |
| Taxes & fees | Government charges and levies that vary by country, state and supplier. |
The wattages below are the averages published by the Centre for Sustainable Energy, a UK energy charity. Your appliances may differ, so check the label on yours and change the watts if you like. Then set roughly how many minutes a day you use each one. The calculator assumes a 30-day month.
Try two experiments. First, set the electric heater to 120 minutes a day and watch it outweigh almost everything else on the list. Second, compare the broadband router (10 watts, on all day) with the kettle (3,000 watts, a few minutes a day): they end up in the same range, because time matters as much as power.
Anything that makes heat is expensive. Anything that runs all day adds up. Everything else is small change.
Fridges, freezers and ovens aren't on the list because they switch themselves on and off to hold a temperature, so their wattage times 24 hours would wildly overstate the cost. For those, use the yearly kWh figure on the appliance's energy label or in its manual.
Heating and cooling are the giants. The EIA's household survey found that space heating and air conditioning made up 52% of US household energy use in 2020, counting all fuels, not just electricity. If your home is heated by gas, that part of the story is on a different bill, but the same logic applies: the thermostat matters more than any gadget.
Standby power is real but smaller than people fear. Lawrence Berkeley National Laboratory estimates that devices drawing power while "off" account for 5–10% of residential electricity use, though most modern products draw under half a watt each in standby. Worth trimming with a switched power strip on a TV-and-console corner; not worth agonizing over a phone charger.
Your bill is usage (kWh) times a unit price, plus a fixed charge. To find the cost of any appliance, multiply its watts by the hours you use it, divide by 1,000 and multiply by your price per kWh. Heat-making appliances (heaters, dryers, showers, kettles) dominate; always-on devices add up quietly; most small electronics barely register. Heating and cooling are usually the biggest lever of all.
Try this: find your actual price per kWh on your last bill, put it into the calculator, and set honest minutes for your three most-used appliances. Then change one habit for the most expensive one and see what it's worth over a year (multiply the monthly saving by 12).
Sources. Appliance wattages and the 26p/kWh UK average (July 2026): Centre for Sustainable Energy, How much electricity am I using?, which also notes that fridges, freezers and ovens cycle on and off. US average consumption (10,791 kWh in 2022): EIA, Frequently Asked Questions. US average residential price (18.16¢/kWh, August 2026): EIA, Electric Power Monthly, Table 5.6.A. Heating and cooling share (52% of household energy, 2020): EIA, Residential Energy Consumption Survey. Standby power (5–10% of residential electricity; most products under 0.5 W): Lawrence Berkeley National Laboratory. Calculator: kWh per month = watts × minutes per day ÷ 60 ÷ 1,000 × 30.