Electricity Cost Calculator

This electricity cost calculator shows what any electrical device costs to run. Enter its power draw in watts, how many hours a day it runs, how many you have and your electricity price. You get the cost per hour, day, month and year, plus the energy used in kilowatt-hours (kWh). It works as a general energy cost calculator for heaters, air conditioners, computers, pumps and anything else that plugs in.

How electricity cost is calculated

Electricity is billed by energy, measured in kilowatt-hours. A kilowatt-hour is the energy used by a 1,000-watt load running for one hour, or exactly 3.6 megajoules (NIST SP 811).

1. Energy per day (kWh) = watts × number of devices × hours per day ÷ 1,000
2. Cost per day = kWh per day × price in ¢/kWh ÷ 100
3. Cost per month = daily cost × 30.42
4. Cost per year = daily cost × 365
5. Cost per hour of use = watts × devices ÷ 1,000 × price ÷ 100

Worked example with the default inputs

Defaults: one 1,500 W device, 4 hours a day, at 18.2¢/kWh, the US residential average rounded from EIA’s 18.16¢ for August 2026 (EIA Electric Power Monthly).

• Energy per day: 1,500 × 4 ÷ 1,000 = 6.00 kWh
• Cost per day: 6 × 18.2 ÷ 100 = $1.09
• Energy per month: 6 × 30.42 = 182.5 kWh
• Cost per month: $33.22
• Cost per year: 6 × 365 × $0.182 = $398.58
• Cost per hour of use: 1.5 kWh × $0.182 = $0.27

Electricity cost reference table

Costs at 18.2¢/kWh, computed with the calculator’s formula.

Device (watts × hours/day)	kWh per month	Cost per month	Cost per year
LED bulb (10 W × 6 h)	1.8	$0.33	$3.99
LED TV (100 W × 5 h)	15.2	$2.77	$33.22
Refrigerator average (150 W × 24 h)	109.5	$19.93	$239.15
Window AC (1,000 W × 8 h)	243.4	$44.29	$531.44
Space heater (1,500 W × 4 h)	182.5	$33.22	$398.58
Central AC, 3-ton (3,500 W × 8 h)	851.8	$155.02	$1,860.04
EV Level 2 charger (7,700 W × 2 h)	468.5	$85.26	$1,023.02

High-wattage devices that run for hours dominate a bill. A central air conditioner on a hot day can use as much as hundreds of LED bulbs. For scale, the average US home used 855 kWh a month in 2023 (EIA Table 5A).

What affects the result

Your actual rate. The US average hides big differences between states and utilities. Find your true price, including fixed charges, with the cost per kWh calculator.

Real power draw versus rated watts. Thermostat-controlled devices (heaters, fridges, AC) cycle on and off, so their average draw is lower than the nameplate. A plug-in watt meter gives the real figure.

Time-of-use pricing. If your utility charges more at peak times, run the calculation once per price period with the hours used in each.

Standby power. Many devices draw a few watts when “off.” Add them as a separate line with 24 hours a day.

How much should electricity cost per month?

The average US home paid $136.84 a month for 855 kWh of electricity in 2023, an average price of 16.00¢/kWh (EIA Table 5A). That is about $4.50 a day. Your normal bill depends mainly on your rate, your climate and whether you heat, cool or charge an EV with electricity.

To check your own figure, multiply your monthly kWh by your price: 855 kWh at 18.2¢ is about $156. A bill far above that usually means high heating or cooling use or a high local rate; find your real rate with the cost per kWh calculator.

Electricity cost for several devices

To cost a whole room or a home office, run the calculator once per device, or set the “number of devices” input for identical items such as light bulbs or monitors. Add the monthly results together. For example, ten 10 W LED bulbs for 6 hours a day cost about $3.32 a month at 18.2¢/kWh, ten times the single-bulb figure in the table. Compare your total with the energy charge on your bill. If the calculator total is far lower, a large load such as heating, cooling or a water heater is probably missing from your list.

Tips to cut electricity costs

• Target the biggest loads first: heating, cooling, water heating, clothes drying and EV charging.
• Look up typical wattages for common appliances in the electricity usage calculator.
• Convert between watts, hours and kWh with the kWh calculator.
• Shift flexible loads, such as EV charging and dishwashers, to off-peak hours on a time-of-use plan.
• See more ways to lower your electric bill, with the yearly saving of each.

History of the electricity bill

The first commercial electric utilities did not charge for kilowatt-hours. When Thomas Edison’s Pearl Street Station began supplying lower Manhattan on 4 September 1882, early electric service was commonly billed by the number of lamps or motors installed. Edison soon used an electrochemical meter, in which an electrolytic cell totalled the current a customer used (history of the electricity meter). The watt itself was only proposed as a unit of power in 1882, and practical recording watt-hour meters arrived in 1889, which made billing for energy actually used, the basis of this calculator, standard practice.

Year	Milestone	Source
1882	Edison’s Pearl Street Station in New York begins supplying about 85 customers on 4 September	IEEE ETHW
1882	C. William Siemens proposes the watt as the unit of power to the British Association	Watt (unit)
1889	Bláthy (Ganz Works) and Elihu Thomson introduce recording watt-hour meters	Electricity meter
1894	Shallenberger’s induction watt-hour meter sets the modern meter design	Electricity meter
1960	The 11th CGPM adopts the watt as the SI unit of power	Watt (unit)

References

• Thompson, A. & Taylor, B. N. (2008). Guide for the Use of the International System of Units (SI). NIST Special Publication 811. doi:10.6028/NIST.SP.811e2008
• BIPM (2019). The International System of Units (SI Brochure), 9th edition. Bureau International des Poids et Mesures. bipm.org

New to the units? Our guide to what a kilowatt-hour is explains kW versus kWh with everyday examples. Lowering your usage also makes it easier to cover your needs with renewable energy such as rooftop solar.