Appliance Energy Use and Cost Calculator

Multiply watts by hours of use, then divide by 1000. A 100 watt device running 5 hours is 100 x 5 / 1000 = 0.5 kWh, because a kilowatt-hour is a thousand watts drawn for one hour.

Look on the rating label or nameplate, usually on the back, base or inside a door. It may be printed directly in watts, or as volts and amps that you multiply together to get watts.

The yearly figure is daily energy times 365 days, and the monthly figure is that yearly total divided by 12. Every month is therefore treated as the same length, so twelve months add back to exactly one year.

Costs are rounded to the nearest cent. A 100 watt device at $0.15/kWh uses $0.075 a day, which rounds up to $0.08. The energy figures keep more decimal places, so the yearly cost stays accurate even when the daily cost rounds.

Use the per kWh rate on your latest bill. Many homes pay somewhere between $0.10 and $0.35 per kWh depending on region, provider and time-of-use plan. If your bill lists several rates, use the one that applies when the appliance runs.

It uses one steady wattage, so it assumes the appliance draws the same power the whole time it runs. For a device that idles for part of the day, run the tool twice, once for active hours and once for the lower standby wattage, then add the two costs.

Yes. Every field accepts decimals, so 0.25 hours for a quick kettle boil or 2.5 hours of television all work. Every value must be greater than zero, otherwise the tool asks for a positive number.

Nameplate watts are a good estimate for resistive loads like heaters and bulbs. Motors, fridges and air conditioners cycle on and off, so their average draw is lower than the peak rating. Treat the result as an upper-bound estimate for those appliances.

No. The calculation runs entirely in your browser, so the wattage, hours and rate you type stay on your device and nothing is uploaded or stored.