How to Calculate Your Appliances’ Electricity Usage (and What They Cost)

Watts and kWh: the difference in one sentence

A watt (W) tells you how much electricity an appliance uses at any given moment. A kilowatt-hour (kWh) tells you how much it has used over time. Think of a car’s speed and the miles it covers. Your utility charges you for kWh: a 1,000 W appliance running for one hour uses 1 kWh.

The formula for an appliance’s electricity usage

The calculation the U.S. Department of Energy recommends, and the same one your utility uses, is:

kWh per day = appliance power (W) × hours used per day ÷ 1,000

A 90 W LED TV that’s on for 5 hours uses 90 × 5 ÷ 1,000 = 0.45 kWh per day. Over a 30-day month that’s 13.5 kWh. If your utility charges 0.15 per kWh, that TV costs you 13.5 × 0.15 = about 2 a month in your currency.

Where to find the wattage, and which units it may come in

The wattage is on a label or nameplate on the back or bottom of the appliance, or on its charger. It isn’t always in watts:

• W or kW. The most common. 1 kW is 1,000 W.
• Amps (A). Multiply them by your home’s voltage: about 110–127 V in the United States, Canada and Mexico, and 220–240 V in the UK, Ireland, Australia and most of Europe. A 5 A appliance at 120 V draws at most 600 W.
• HP. The rating of motors, such as a water pump. 1 HP is 745.7 W, but that’s what the motor delivers: what it draws from the grid is usually a bit more.
• kWh per year. The figure on the energy label of fridges, freezers and washing machines. For those appliances it’s the most reliable number, because it already reflects how they really run. Divide it by 365 to get one day’s usage.
• BTU or frigories (air conditioners). Careful: they measure how much the unit cools, not how much electricity it draws. To go from BTUs to watts you divide by the unit’s efficiency (its EER): a 12,000 BTU unit with an EER of 12 draws 1,000 W. Frigories, used in Argentina and Uruguay, are about 3.97 BTU each.

The figure on the label is usually the maximum: many appliances draw less most of the time.

Appliances with a thermostat: the % of time running

A fridge is plugged in 24 hours a day, but its compressor switches on when it needs to cool and off once it reaches the set temperature. Air conditioners, ovens and irons do the same. That’s why, for those appliances, you should only count the share of time they’re actually running.

How big is that share? Official sources don’t agree on one number. Argentina’s electricity regulator (ENRE) works out that a 200 W fridge-freezer uses 90 Wh in an hour, meaning it runs 45% of the time, and that irons and ovens run half the time. The U.S. Department of Energy suggests counting one third of the time for a fridge. It depends on the model, its age, how hot it is and how often the door is opened. If you want the exact figure for your fridge, use the kWh per year on its energy label or measure it for a full day with a plug-in energy monitor.

Where to find the price per kWh on your bill

Your bill shows the kWh you used in the billing period and what you were charged for that energy. Divide the energy charge by the kWh and you have the price of each kWh. Don’t use the bill total: it includes fixed charges and taxes that don’t depend on how much you use.

Many utilities charge more per kWh above a certain usage (tiered rates) or depending on the time of day. If that’s your case, use the price of the tier you usually fall into.

Worked example: what a home uses in a month

These are the appliances in a simple home, with the wattages and % running from the ENRE table (electric showers aren’t in that table: the 5,500 W is a common label value):

At 0.15 per kWh, these appliances cost about 27.11 a month. The fridge is the biggest user, and right behind it comes the electric shower, even though it’s used for only 18 minutes a day. If that fridge were an inverter fridge-freezer (ENRE counts it as running 17.5% of the time), it would use 0.84 kWh per day instead of 2.16.

How much does a typical home use? It depends a lot on the country

There’s no single figure that works worldwide, because climate, home size and, above all, whether electricity is used for heating or cooling all vary:

• In the European Union, according to the Odyssee-Mure project, electricity use per dwelling ranges from 1.8 MWh a year in Romania (about 150 kWh a month) to 8.5 MWh in Sweden (about 710 kWh a month), with an average of 3.6 MWh (about 300 kWh a month). The differences come mostly from electric heating, how many appliances each home has and how efficient they are.
• In the United States, a home used an average of 861 kWh a month in 2023, according to the Energy Information Administration. Central air conditioning, tumble dryers and electric heating are very common there.

For Latin American countries we haven’t found a comparable official per-home figure, and we’d rather not give a number without a source. Either way, the best benchmark is your own: many bills include a chart of your usage over recent months.

Standby power

Many devices keep drawing power when switched off with the remote: TVs, set-top boxes, microwaves with a clock and chargers left plugged in. Each uses little, but it adds up. Lawrence Berkeley National Laboratory estimated in 1997 that standby use was about 5% of a home’s electricity. A power strip with a switch lets you turn several off at once. We cover which use the most and what’s worth unplugging in standby power.

How to check with a plug-in energy monitor

If you want to know what an appliance really uses, a plug-in energy monitor is cheap and very useful: plug it into the wall, plug the appliance into it, and it shows the watts and the kWh used so far. For a fridge, leave it in place for 24 hours and you’ll have its real usage for a day, compressor cycles included.

What you shouldn’t do is open your breaker panel or touch wiring to take measurements: that’s a job for an electrician.