Power Consumption Calculator

Calculate electricity usage in watts, kilowatt-hours, and estimated cost for any appliance or device.

Power Consumption Calculator tool

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Example

Input: 1500 W space heater, 3 hours per day, electricity $0.16 per kWh

Result: 4.5 kWh per day ($0.72), 136.875 kWh per month ($21.90), 1,642.5 kWh per year ($262.80)

1,500 W x 3 h / 1,000 = 4.5 kWh per day; 4.5 x 365 = 1,642.5 kWh per year, and 1,642.5 x $0.16 = $262.80.

  1. Enter the wattage of the appliance or device (check the label or spec sheet for this value).
  2. Set the estimated daily usage hours for the device.
  3. Enter your local electricity rate in cost per kilowatt-hour (found on your utility bill).
  4. View the calculated energy consumption in kWh and estimated cost for daily, monthly, and yearly periods.
  5. Compare multiple devices by adjusting the wattage to find the most cost-effective option.

How Much Electricity Does a Device Use?

Energy use in kilowatt-hours (kWh) equals watts times hours of use, divided by 1,000. Multiply the kWh by your electricity rate to get the cost. A 1,500 W space heater running 3 hours a day uses 4.5 kWh a day. At $0.16 per kWh, that is $0.72 a day or $262.80 a year.

A kilowatt-hour is the unit on your power bill. It is 1,000 watts used for one hour, or 100 watts for ten hours. Enter a device's wattage, how many hours a day it runs, and your rate per kWh. The tool shows energy and cost per day, per month and per year. A month here is an average of 365 / 12 days, about 30.4, so twelve months add up to exactly one year.

You can find the wattage on the label or in the manual. For devices that cycle on and off, like fridges and air conditioners, the label wattage overstates real use. A plug-in power meter gives a truer number. Your rate is on your bill as the price per kWh. Some bills add fixed fees and taxes, so divide the total by the kWh used for an all-in rate. Use the results to find the devices that cost the most, or to check how fast a more efficient model pays for itself. To convert kWh to other energy units, use the Energy Converter.

Formula / How It Works

Energy (kWh) = Power (W) x Time (hours) / 1000 | Cost = Energy (kWh) x Rate ($/kWh)

Frequently Asked Questions

Multiply watts by hours used, divide by 1,000 to get kWh, then multiply by your rate. A 100 W TV used 5 hours a day uses 0.5 kWh a day. At $0.15 per kWh, that is $0.075 a day, about $2.28 a month or $27.38 a year.
Watts measure power, the rate at which a device uses energy at any moment. Kilowatt-hours measure energy, the total used over time. A 1,000 W heater running for 1 hour uses 1 kWh. The same heater running for 30 minutes uses 0.5 kWh. Power companies bill you for kWh.
Standby draw is often 1 to 5 W. A 5 W standby load running 24 hours a day uses 0.12 kWh a day, or 43.8 kWh a year. At $0.15 per kWh, that is about $6.57 a year per device. Enter your own wattage and rate here to check.
Bills include fixed charges, delivery fees and taxes on top of the energy price. Many devices also draw more or less than their label says. For a closer match, divide your bill total by the kWh used to get an all-in rate, and measure real wattage with a plug-in meter.

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