How much electricity an appliance uses in a month comes down to two numbers: how much power it draws while running and how many hours it actually runs. A refrigerator draws little power but is plugged in all month, while a space heater draws a lot of power for a few hours a day. Multiply the wattage by the hours, divide by 1,000, and you get kilowatt-hours (kWh), the unit your utility bills you in. For the biggest appliances, the most reliable figure is already printed on the yellow EnergyGuide label.
For scale, the U.S. Energy Information Administration (EIA) reports in its household electricity FAQ that the average residential utility customer bought 10,791 kWh in 2022, about 899 kWh per month. That average hides a wide spread: Louisiana had the highest purchases per residential customer that year at 14,774 kWh and Hawaii the lowest at 6,178 kWh. EIA also notes that rooftop solar systems, common in Hawaii, reduce what a household buys from the grid, so purchases can understate actual use. The rest of this guide shows how to work out where your own kWh go, one appliance at a time, and how to sanity-check the result against your bill.
Watts versus kilowatt-hours
A watt measures the rate at which a device draws power at a given moment. A kilowatt-hour measures energy used over time: 1,000 watts sustained for one hour. That is why "how many watts does it use?" only answers half the question. A 1,500-watt hair dryer used for ten minutes a day can end up using less energy over a month than a modest device that never switches off, simply because time is the other half of the equation.
Keeping the two units apart also explains why appliance charts online disagree so much. Some list nameplate wattage, some list typical monthly kWh, and some multiply the nameplate figure by every hour in the month. Those numbers are not comparable, and the last method can overstate refrigerator use nearly threefold, as the next section shows.
The watts × hours ÷ 1,000 formula
A Virginia Cooperative Extension publication, Estimating Appliance and Home Electronic Energy Use (Virginia Tech, February 2020), gives the standard method: wattage × hours used per day ÷ 1,000 = daily kWh. Multiply by the number of days the appliance is used to get monthly or annual consumption, then multiply by your rate per kWh to get the cost. The same publication notes that wattage is usually stamped on the bottom, back or nameplate of the appliance. To apply it to something in your home:
- Find the wattage on the nameplate, or multiply the listed amps by the voltage.
- Estimate the hours per day the appliance actually runs, not the hours it sits plugged in.
- Multiply watts by hours and divide by 1,000 to get daily kWh.
- Multiply daily kWh by the days of use in a month.
- Multiply monthly kWh by your price per kWh for an approximate cost.
Step one has a useful fallback. According to the publication, most U.S. appliances run on 120 volts, while larger ones such as clothes dryers and electric cooktops use 240 volts. If a label lists only amps, multiply them by the right voltage. The publication also notes that the actual power drawn depends on the setting in use, so a nameplate figure multiplied by every running hour usually gives an upper limit.
Why the refrigerator estimate goes wrong
Refrigerators are the classic trap. The extension publication explains that a refrigerator, although always on, cycles on and off to hold its temperature, and suggests dividing the time it is plugged in by three to estimate full-power running hours. As a hypothetical example, a refrigerator with a 150-watt nameplate multiplied by 720 hours gives 108 kWh a month. Using a third of the hours drops that to 36 kWh. If its EnergyGuide label says 450 kWh per year, the measured monthly figure is 37.5 kWh.
Start with the EnergyGuide label
For major appliances you often do not need the formula at all. The Federal Trade Commission's Energy Labeling Rule requires yellow EnergyGuide labels that state a product's estimated annual operating cost and energy consumption. They appear on clothes washers, dishwashers, refrigerators, freezers, water heaters, room air conditioners, central air conditioners, furnaces, boilers, heat pumps, pool heaters and televisions. Under the rule, manufacturers must also post a copy of each model's label on a publicly accessible website.
The table below shows where to find a usable number for common appliances and how to turn it into monthly kWh. The example values in the last column are hypothetical and only illustrate the arithmetic; nameplate ranges in the middle rows come from the Virginia Cooperative Extension list of typical wattages.
| Appliance | Best source for the number | How to get monthly kWh | Hypothetical example |
|---|---|---|---|
| Refrigerator | EnergyGuide label, kWh per year | Annual kWh ÷ 12 | 450 kWh/yr → 37.5 kWh |
| Television | EnergyGuide label, kWh per year | Annual kWh ÷ 12 | 120 kWh/yr → 10 kWh |
| Clothes dryer (1,800–5,000 W) | Nameplate watts | Watts × hours ÷ 1,000 | 3,000 W × 12 h → 36 kWh |
| Space heater (750–1,500 W) | Nameplate watts | Watts × hours ÷ 1,000 | 1,500 W × 120 h → 180 kWh |
| Microwave (750–1,100 W) | Nameplate watts | Watts × hours ÷ 1,000 | 1,000 W × 5 h → 5 kWh |
The pattern is clear: a label figure already reflects a standard test, while a nameplate figure needs an honest estimate of running time. Keep in mind that the label's yearly cost is calculated with a national average electricity price, which the FTC rule specifies, so your own cost will differ with your rate. Take the kWh line from the label and apply your own price to it.
Worked examples with a current U.S. price
To turn kWh into dollars you need a rate. EIA's Electric Power Monthly puts the average U.S. residential price at 18.31 cents per kWh for July 2026, a preliminary figure released on September 24, 2026. State averages vary widely around it, so treat the following hypothetical examples as an order of magnitude and swap in the rate printed on your own bill.
Take the hypothetical space heater from the table: 180 kWh a month at 18.31 cents comes to about $32.96. The refrigerator labelled at 450 kWh a year works out to roughly $6.87 a month, or about $82 over the year. A hypothetical 1,500-watt kettle used for ten minutes a day adds 7.5 kWh, around $1.37 a month. The heater dominates because it combines high wattage with long hours, which is exactly the combination to look for when a bill jumps.
Small always-on loads deserve a line too. The extension publication describes "phantom loads": many devices keep drawing a little power when switched off, which you can avoid by unplugging them or using a power strip with a switch. A hypothetical device drawing 5 watts around the clock uses 3.6 kWh a month, about 66 cents. Ten such devices add 36 kWh, roughly the same as the labelled refrigerator above.
What national averages tell you
EIA's Electricity use in homes page, based on the 2020 Residential Energy Consumption Survey, shows where household electricity goes. Air conditioning took 19% of residential site electricity in 2020, space heating 12% and water heating 12%. Lighting and refrigerators were the next two largest end uses. The page also notes that end-use shares shift from year to year with the weather, so a hot summer or cold winter changes the picture.
Refrigerators are worth a second look because so many homes have more than one. According to the same EIA page, 99% of U.S. homes had a refrigerator in 2020 and 34% had two or more. The most-used refrigerator cost about $87 on average to run that year, a second refrigerator about $66, and a separate freezer $74. If an old fridge in the garage is mostly holding drinks, its share of the bill is easy to calculate with the label method above.
Comparing models before you buy
The same arithmetic helps when you are choosing a new appliance. The FTC rule requires the EnergyGuide label to show a range comparing the highest and lowest energy cost of similar models, so you can see where a model sits before you look at its price tag. Because that cost is based on a national average rate, convert the kWh figure with your own rate for a fairer comparison.
As a hypothetical example, suppose one refrigerator is labelled at 450 kWh a year and a similar model at 600 kWh. The difference is 150 kWh a year, about $27.47 at the July 2026 average of 18.31 cents. Over ten years at that same rate, the gap adds up to roughly $275. Prices change, so read it as a rough way to weigh a higher purchase price against running costs.
How to make your estimate more accurate
The quality of the result depends on the quality of the inputs. Multiplying a nameplate figure by the whole month inflates the total, while guessing hours without tracking them tends to shrink it. These checks tighten the numbers, and most of them need no special equipment:
- Use labels first: For anything with an EnergyGuide label, use the annual kWh figure rather than nameplate wattage.
- Time your actual use: Track how long the dryer, oven and heater run for a week, then scale to a month.
- Check the voltage: Multiply amps by 120 volts for most plug-in devices and by 240 volts for dryers and electric cooktops.
- Measure stubborn devices: The extension publication describes reading current with a clamp-on ammeter while the device runs, following the meter maker's safety instructions.
- Account for seasons: Estimate heating and cooling separately for the months you actually use them.
Once you have a list, add up the monthly kWh and compare the total with your latest bill. A total far below the bill usually means a high-wattage appliance has been underestimated, or a load such as a water heater is missing. A total well above the bill usually means a nameplate figure was multiplied by the full month. Water heaters show why a missing load matters: the extension publication lists a 40-gallon electric water heater at 4,500–5,500 watts, so a hypothetical unit running at 4,500 watts for one hour a day adds 135 kWh a month, more than three times the labelled refrigerator above.
Turning your kWh into a bill estimate
With your monthly total in hand, you can turn it into a cost. NumerSpace's electricity bill calculator multiplies kWh by a unit price and a separate distribution charge, then adds VAT. It was built around Turkish bills, so its fields are labelled in Turkish lira and the VAT default reflects Turkey. For a U.S. bill, enter your all-in rate as the unit price and set the distribution charge and VAT to zero; the arithmetic is the same.
If lighting is on your list, the lighting calculator estimates the lumens a room needs and how many LED bulbs that takes, which gives you a realistic wattage to plug into the formula. More household tools are collected on the Home and Living page.