How to use it
- Pick a typical appliance or enter its wattage.
- Enter hours of use per day and the number of days.
- Enter your electricity rate in dollars per kWh.
- Read the kWh used and the cost, including yearly totals.
How to calculate electricity cost
kWh = watts × hours ÷ 1,000
Cost = kWh × price per kWh
Example: a 1,500-watt space heater running 5 hours a day for 30 days:
- 1,500 × 5 × 30 / 1,000 = 225 kWh
- At $0.17 per kWh: 225 × 0.17 = $38.25 for the month
The calculator also shows daily and yearly use and cost, and handles several identical devices at once. Everything is calculated in your browser.
Typical appliance wattages
| Appliance | Typical watts |
|---|---|
| LED bulb | 9 |
| Laptop | 50 |
| TV | 100 |
| Desktop computer | 250 |
| Window air conditioner | 900 |
| Microwave | 1,000 |
| Space heater, kettle, hair dryer | 1,500 |
| Induction cooktop burner | 1,800 |
These are rough figures. Check the label on your device (often on the back or bottom) or the manual for its rated wattage. If only amps are listed, multiply by the voltage: 12 A × 120 V = 1,440 W.
Finding your rate
Your electric bill lists the price per kWh, sometimes split into a supply (generation) charge and a delivery charge. Add them together and divide by 100 if the bill shows cents: 17.2 cents = $0.172. Rates vary widely by state and utility, and some plans charge more at peak times, so use your own number for an accurate result. Fixed monthly service fees do not depend on usage and are not included.
Standby power
Many devices draw power even when they are "off": TVs, game consoles, chargers and anything with a clock or remote. Enter a standby wattage and the calculator adds it for the hours the device is not in use.
A device drawing 5 W on standby all year uses 5 × 24 × 365 / 1,000 = 43.8 kWh, about $7.45 at $0.17 per kWh. Across a whole house, standby loads add up. A smart power strip or unplugging rarely used devices cuts this waste.
Appliances that cycle
Refrigerators, freezers, air conditioners, water heaters and heaters with thermostats switch on and off, so they rarely draw their full rated power all day. For these, the yearly kWh on the EnergyGuide label is a better starting point. A refrigerator rated at 400 kWh a year costs about $68 a year at $0.17 per kWh.
If you want to measure a plug-in device directly, an inexpensive plug-in watt meter shows actual usage over days or weeks.
Ways to cut your bill
- Replace incandescent bulbs with LEDs; a 9 W LED gives about the same light as a 60 W incandescent.
- Use a programmable thermostat and seal drafts.
- Run full loads in dishwashers and washing machines, and wash in cold water.
- Look for ENERGY STAR models when replacing appliances.
For space heating, air conditioning and other large loads, small changes in hours of use make the biggest difference. Use the calculator to compare options before you buy.
Example comparison: an old 60 W incandescent bulb used 5 hours a day costs about $18.62 a year at $0.17 per kWh; a 9 W LED giving similar light costs about $2.79. Ten bulbs swapped saves roughly $158 a year, and LEDs also last many times longer, so you replace them far less often.
Frequently asked questions
How do I calculate kWh from watts?
Multiply watts by hours of use and divide by 1,000. A 100 W TV used 4 hours uses 0.4 kWh.
How much does it cost to run a space heater?
A 1,500 W heater costs about $0.26 an hour at $0.17 per kWh, or $38.25 a month at 5 hours a day.
Where do I find my electricity rate?
On your electric bill, as cents or dollars per kWh. Add supply and delivery charges if they are listed separately.
Does the calculator include standby power?
Yes, if you enter a standby wattage; it applies to the hours the device is not in use.
Why is my fridge's real usage lower than watts × 24?
Refrigerators cycle on and off. Use the yearly kWh on the EnergyGuide label for a better estimate.
Last updated: November 12, 2026