How to calculate electricity cost
Cost = kWh × Rate per kWh
A 1,500-watt space heater running 4 hours a day uses 1,500 × 4 ÷ 1,000 = 6 kWh a day. At 17 cents per kWh that's about $1.02 a day, or roughly $31 a month.
Finding an appliance's wattage
Look for a label on the back or bottom of the appliance, or in the manual. If it lists amps instead of watts, multiply amps by volts (120 V for most U.S. outlets). Appliances with thermostats or compressors — refrigerators, air conditioners, water heaters — cycle on and off, so their average draw is well below the label rating. For those, use an average wattage (the defaults above are typical averages) or measure with a plug-in energy meter.
Typical wattages
- LED bulb: 8–12 W · Laptop: 30–60 W · TV: 50–150 W · Desktop computer: 100–250 W
- Refrigerator: 100–250 W running, about 40–70 W averaged over a day
- Microwave: 1,000–1,200 W · Space heater: 1,500 W · Clothes dryer: 2,000–5,000 W
- Central air conditioner: 2,000–4,000 W while running
Your bill also includes fixed monthly charges and taxes, so your total bill will be higher than the energy cost shown here.
What common appliances cost to run
At 17 cents per kWh, with typical daily use:
| Appliance | Power | Daily use | Cost per month |
|---|---|---|---|
| LED light bulb | 10 W | 5 hours | $0.26 |
| Television | 100 W | 5 hours | $2.59 |
| Refrigerator | 60 W average | 24 hours | $7.45 |
| Clothes dryer | 3,000 W | 30 minutes | $7.76 |
| Desktop computer | 200 W | 8 hours | $8.27 |
| Space heater | 1,500 W | 4 hours | $31.03 |
| Window air conditioner | 900 W | 8 hours | $37.23 |
The pattern is clear: anything that heats or cools dominates the bill. Lighting and electronics cost comparatively little, so the biggest savings come from heating, cooling, hot water and laundry.
What is a kilowatt-hour?
A kilowatt-hour (kWh) is the unit your electric company bills you for. It's the energy used by 1,000 watts running for one hour — or 100 watts for 10 hours, or a 10-watt bulb for 100 hours. Watts measure how fast energy is being used; kilowatt-hours measure how much has been used.
Frequently asked questions
Where do I find my electricity rate?
On your bill, usually listed as a price per kWh. If your bill shows several charges, divide the total amount by the total kWh used for an all-in average rate. Rates vary widely by region — from around 11 cents to over 40 cents per kWh across the United States.
Do devices use power when they're switched off?
Many do. TVs, game consoles, chargers and anything with a clock, remote control or standby light draw a small "phantom" or standby load. Individually it's a watt or two, but across a household it can add up to several percent of the bill. A power strip you can switch off stops it.
What are time-of-use rates?
Some utilities charge more during peak hours, often late afternoon and evening, and less overnight. If you're on such a plan, running the dishwasher, laundry or an electric-car charger off-peak can cut costs noticeably. Enter your peak and off-peak rates separately to compare.
How can I measure an appliance's real consumption?
A plug-in electricity usage monitor sits between the appliance and the outlet and shows exactly how many kWh it uses over time. It's the best way to handle appliances that cycle on and off, such as refrigerators and freezers.
How much does it cost to charge an electric car?
Multiply the battery energy added by your rate. Adding 50 kWh at 17 cents costs $8.50. A typical electric car uses around 0.25–0.35 kWh per mile, which works out to roughly 4 to 6 cents a mile at that rate.