How to use the electricity calculator
Enter the appliance's power in watts (W), the number of hours it runs per day, and how many appliances you have. Then enter your electricity rate in price per kilowatt-hour (kWh). The calculator estimates the energy used and the cost per day, month, and year.
- Enter the appliance power in watts.
- Enter the average number of hours the appliance runs each day.
- Enter the quantity if you have more than one of the same appliance.
- Enter your electricity rate per kWh.
- Review the estimated daily, monthly, and yearly cost.
How electricity cost is calculated
Electricity is billed by the kilowatt-hour (kWh), which measures how much energy is used over time. One kilowatt-hour is the energy used by a 1,000-watt appliance running for one hour.
To calculate energy usage, multiply an appliance's power in watts by the number of hours it runs and by the quantity of appliances, then divide by 1,000:
Energy (kWh) = Watts × Hours × Quantity ÷ 1000 Watts measure electrical power, while kilowatt-hours measure the energy consumed over time. For calculations involving watts, volts, amps, and resistance, use our Electrical Power Calculator.
Once you know the energy used, multiply the kWh by your electricity rate to estimate the cost:
Cost = Energy (kWh) × Electricity Rate For example, a 150-watt appliance running for 24 hours per day at $0.15 per kWh uses 3.6 kWh per day. At that rate, it costs about $0.54 per day, $16.20 over 30 days, or $197.10 over 365 days.
Electricity usage examples
The amount of electricity an appliance uses depends on its power rating and how long it operates. For example, a higher-powered appliance can use less energy than a lower-powered appliance if it runs for significantly less time.
| Appliance | Example Power | Usage | Energy Per Day |
|---|---|---|---|
| LED light bulb | 10 W | 5 hours | 0.05 kWh |
| Television | 100 W | 4 hours | 0.40 kWh |
| Refrigerator | 150 W* | 24 hours | 3.60 kWh* |
| Space heater | 1,500 W | 2 hours | 3.00 kWh |
| Microwave | 1,200 W | 15 minutes | 0.30 kWh |
*These are simplified examples. Appliances such as refrigerators and air conditioners normally cycle on and off, so their actual average energy use can be substantially different from a simple calculation based on their rated wattage.
Finding your electricity rate
Your electricity rate is usually shown on your utility bill as a price per kilowatt-hour. Look for a line showing the energy charge, electricity supply rate, or cost per kWh.
Rates vary by location, provider, plan, and time of use. Some electricity plans also use different rates at different times of day, so use the rate that best matches the period you are estimating.
What affects actual electricity cost?
An appliance's wattage alone does not determine how much electricity it costs to operate. Actual consumption depends on how long the appliance runs, whether it operates continuously, its efficiency, and how its controls are set.
Similar power and energy calculations apply to battery-powered devices. If you're working with battery capacity, runtime, or charging time, see our Battery Calculator.
Your final electricity bill may also include tiered or time-of-use rates, taxes, fixed charges, delivery charges, and other fees. This calculator estimates the energy cost based on the rate you enter and does not reproduce a utility bill.
Frequently asked questions
Where do I find my appliance's wattage?
Check the label or nameplate on the appliance, usually on the back, bottom, or side, or check the owner's manual or product specifications. If the appliance lists amps and volts instead of watts, you can estimate watts by multiplying volts by amps: watts = volts × amps.
How do I calculate kWh from watts?
Multiply watts by the number of hours the appliance runs, then divide by 1,000. For example, a 500-watt appliance running for 4 hours uses 2 kWh: 500 × 4 ÷ 1,000 = 2 kWh. If you have multiple identical appliances, multiply by their quantity as well.
How much does it cost to run an appliance for one hour?
Divide the appliance's wattage by 1,000 to convert watts to kilowatts, then multiply by your electricity rate. For example, a 1,000-watt appliance running for one hour uses 1 kWh. At $0.15 per kWh, that hour costs $0.15.
What if I only use an appliance for part of an hour?
Enter the equivalent number of hours as a decimal. For example, 30 minutes is 0.5 hours, 15 minutes is 0.25 hours, and 45 minutes is 0.75 hours. The calculator supports fractional hours.
Why don't the monthly and yearly numbers exactly match my bill?
This calculator uses a fixed 30-day month and 365-day year and assumes the appliance is used consistently. Your actual bill may cover a different number of days and may include tiered rates, time-of-use pricing, taxes, fixed charges, or other fees. Appliance usage can also vary from day to day.
What's the difference between watts and kilowatt-hours?
Watts measure power, or how quickly an appliance uses energy. Kilowatt-hours measure energy, or the total amount used over a period of time. A 1,000-watt appliance running for one hour uses 1 kWh.
Does an appliance's rated wattage always equal its actual electricity use?
No. The wattage shown on an appliance is its rated or specified power draw and may not represent its average consumption. Refrigerators, air conditioners, heat pumps, and other appliances can cycle on and off. Variable-speed appliances can also change their power draw while operating. For the most accurate estimate, use an average or measured power consumption when available.