Electricity Calculator
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Choose a typical appliance or enter your own wattage and hours of use, then your electricity price per kWh. The electricity calculator estimates the energy used and its cost per day, month and year.
Units of electricity:
Power is the rate at which a device uses energy, measured in watts (W). One kilowatt (kW) is 1,000 watts. The power rating on an appliance's label is the most it draws when running flat out; many devices, such as refrigerators, air conditioners and heaters with thermostats, cycle on and off and draw less on average, which is what the run-level percentage accounts for.
Energy is power multiplied by time. Utilities bill for energy in kilowatt-hours (kWh): one kWh is the energy used by a 1,000-watt device running for one hour, or a 100-watt device for ten hours. A kilowatt-hour equals 3.6 million joules, the SI unit of energy. Large quantities are counted in megawatt-hours (MWh, 1,000 kWh) and gigawatt-hours (GWh, one million kWh), the scale of power plants and cities.
Voltage (volts, V) is the electrical pressure that pushes current, and current (amperes, A) is the rate of flow of charge. For resistive devices, power equals voltage times current, so a kettle drawing 12.5 A on a 120 V circuit uses 1,500 W. In homes with AC power, many electronic and motor-driven devices also have a power factor below 1, so their real power in watts is less than volts times amps; household meters bill only the real power.
Heating and cooling equipment is often rated in other units. Air conditioners are sized in BTU per hour (1 W ≈ 3.412 BTU/h) or in tons of refrigeration, where one ton is 12,000 BTU/h, the cooling needed to melt a ton of ice in a day. Note that an air conditioner's cooling capacity is not its electrical input: an efficient unit moves three or more units of heat for each unit of electricity, so a 12,000 BTU/h unit may draw only around 1,000 to 1,200 W. Motors and pumps are rated in horsepower, about 746 W for mechanical horsepower or 735.5 W for the metric horsepower this calculator uses.
The average US home used about 10,500 kWh in a recent year according to the Energy Information Administration, or roughly 875 kWh a month, with space heating and cooling, water heating and refrigeration the largest uses. Residential prices differ widely by state, from around 10 cents to over 40 cents per kWh, so use the rate printed on your bill, including delivery charges, for the most accurate estimate.
Energy (kWh) = power (W) × share of power used × hours ÷ 1,000 · Cost = kWh × price per kWh
A month is taken as 1/12 of a year (about 30.4 days).
Amount of energy used by common appliances:
The table gives typical wattages and usage patterns for common household devices and the energy they use per month. Actual figures depend heavily on the model, its efficiency rating, settings and how it is used, so check the label or measure with a plug-in energy monitor for a precise number.
| Appliance | Typical power | Typical use | Energy per month |
|---|---|---|---|
| Central air conditioner (3 ton) | 3,000 – 3,500 W | 8 h/day in summer | about 800 kWh |
| Refrigerator (modern, ENERGY STAR) | 100 – 200 W while running | Cycles all day | 30 – 50 kWh |
| Electric water heater | 4,500 W | 2 – 3 h/day | 300 – 400 kWh |
| Clothes dryer | 3,000 W | 5 loads/week | about 60 kWh |
| Electric oven | 2,400 W | 1 h/day at half power | about 35 kWh |
| Electric vehicle (1,000 miles) | 7 – 11 kW charger | about 4 h/week | 250 – 350 kWh |
| LED TV (55 inch) | 60 – 100 W | 5 h/day | 10 – 15 kWh |
| Laptop | 30 – 60 W | 8 h/day | 7 – 15 kWh |
| LED bulb (60 W equivalent) | 8 – 10 W | 5 h/day | about 1.4 kWh |
Energy saving tips:
Heating and cooling usually make up the biggest share of a home's energy use, so they offer the biggest savings. The US Department of Energy notes that setting the thermostat back 7 to 10 °F for eight hours a day can save up to about 10% a year on heating and cooling. A smart or programmable thermostat does this automatically. Seal air leaks around doors, windows and ducts, add attic insulation, and change HVAC filters regularly.
Lower the water heater to 120 °F (49 °C), wash clothes in cold water, and run dishwashers and washers only with full loads. Air-dry laundry when you can; the clothes dryer is one of the hungriest appliances in the house.
Replace remaining incandescent and halogen bulbs with LEDs, which use about 75% to 80% less energy and last many times longer. Turn off lights in empty rooms, or fit occupancy sensors in rooms where they are often left on.
Many electronics draw standby power around the clock. Unplug chargers and devices you rarely use, or plug entertainment centers and computer setups into smart power strips that cut power when the main device is off. When replacing appliances, choose ENERGY STAR certified models, and compare the yellow EnergyGuide label's estimated yearly cost between models.
Finally, check your utility's rate plans. Time-of-use plans charge less overnight and on weekends, which can make running the dishwasher or charging an electric car at night noticeably cheaper.
| Change | Typical saving |
|---|---|
| Thermostat set back 7–10 °F for 8 hours a day | Up to about 10% of heating and cooling costs |
| Incandescent bulb to LED | About 75–80% less energy per bulb |
| Washing laundry in cold water | Most of the energy per load, which goes into heating water |
| Water heater from 140 °F to 120 °F | Reduces standby heat loss and scalding risk |
| Smart power strip for entertainment center | Cuts standby draw when devices are off |
Frequently asked questions
How do I calculate the cost to run an appliance?
Multiply the wattage by the hours used, divide by 1,000 to get kWh, then multiply by your price per kWh. A 1,500 W heater run 4 hours uses 6 kWh, which costs $0.90 at $0.15 per kWh.
What is a kilowatt-hour?
The energy used by a 1,000-watt device running for one hour. It is the unit on your electricity bill.
How much does it cost to run a refrigerator?
A modern refrigerator uses about 400 to 600 kWh a year, roughly $60 to $90 at 15 cents per kWh. Older models can use twice as much.
Do devices use power when turned off?
Many do. Standby or phantom loads from chargers, TVs, game consoles and appliances with displays can add up to 5% to 10% of a household's electricity use.
How do I estimate my monthly electricity bill?
Add up each appliance's monthly kWh, or take the total from a past bill, multiply by your price per kWh and add any fixed monthly charge. At the US average of about 875 kWh a month and 15 cents per kWh, the energy cost is about $131. Use the rate on your own bill, including delivery charges, since prices range from around 10 to over 40 cents per kWh by state.
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