Watts, kilowatt-hours and your bill
Watts measure how fast a device uses power; kilowatt-hours (kWh) measure how much energy it used over time, and kWh is what your utility bills you for. A 1,000-watt appliance running for one hour uses 1 kWh. The Virginia Cooperative Extension guide to appliance energy use gives the same recipe used here: wattage × hours used per day ÷ 1,000 = daily kWh, then multiply by your rate.
If the label only shows amps, multiply amps by the voltage to estimate watts: a 12.5 A device on a 120 V circuit draws about 1,500 W. The Virginia Tech guide notes that most US appliances use 120 volts; large ones such as electric dryers and ranges are usually on 240 V circuits.
What rate to use
The default rate is 18.19 cents per kWh, the US average residential price for January through July 2026 in the US Energy Information Administration's Electric Power Monthly (preliminary figures). For comparison, the same period in 2025 averaged 17.01 cents, and July 2026 alone was 18.31 cents.
Prices vary a lot by state and utility, so the best number is on your own bill: divide the energy charges by the kWh used, or look for the per-kWh rate. Include delivery or distribution charges that are billed per kWh, since they scale with use too.
Getting a realistic answer
The nameplate wattage is a maximum. Devices that cycle, such as refrigerators, freezers and anything on a thermostat, draw full power only part of the time. The Virginia Tech guide suggests dividing a refrigerator's plugged-in hours by three to estimate the hours it actually runs at full wattage.
For the most accurate number, measure: a plug-in electricity usage monitor shows the actual kWh a plug-in device uses over a day or a week. The guide also warns about phantom loads, the small amount of power many devices draw even when switched off.
The formulas
kWh per day = W × n × h ÷ 1,000kWh per year = kWh per day × d × 365 ÷ 7Cost = kWh × rate ÷ 100W = A × V (when you only know amps)- W = power in watts; n = number of devices
- h = hours used per day; d = days used per week
- rate = price in cents per kWh
- A = current in amps; V = voltage in volts
Example: a 1,500 W space heater, 4 hours a day
- Daily energy: 1,500 × 4 ÷ 1,000 = 6 kWh.
- Daily cost at 18.19¢: 6 × 0.1819 = $1.09.
- Yearly energy if used every day: 6 × 365 = 2,190 kWh, costing 2,190 × 0.1819 = $398.36.
- Average month: 2,190 ÷ 12 = 182.5 kWh, or $33.20.
Frequently asked questions
How do I calculate the cost to run an appliance?
Multiply watts by hours of use and divide by 1,000 to get kWh, then multiply by your rate. A 1,500 W heater for 4 hours uses 6 kWh, which costs $1.09 at 18.19 cents per kWh.
How much does it cost to run an LED bulb?
A 10 W LED bulb on for 5 hours a day uses 10 × 5 × 365 ÷ 1,000 = 18.25 kWh a year, about $3.32 at 18.19 cents per kWh.
What is the average electricity rate in the US?
According to the EIA, the US average residential price was 18.19 cents per kWh for January through July 2026 (preliminary), up from 17.01 cents for the same months of 2025.
How do I convert amps to watts?
Watts ≈ amps × volts. A 12.5 A appliance on 120 V is about 1,500 W, and a 10 A load on 240 V is about 2,400 W.
Why is my bill higher than this estimate?
Your bill includes every device in the home, fixed monthly charges and any taxes or fees. Thermostat-controlled loads like heating and cooling also vary with the weather.
Sources
Last reviewed for 2026. How we calculate.