Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate the running cost of any electrical device or appliance from its wattage, usage hours, and your utility rate.
Every electrical device's running cost follows the same basic formula regardless of what it is -- a space heater, a window AC unit, a refrigerator, or any other appliance -- so this single general-purpose calculator covers appliance energy cost questions broadly rather than needing a separate tool per device type.
Enter the device's power draw in watts (check its label or spec sheet), hours used per day, number of days you're estimating for, and your utility's price per kWh (check a recent bill for your exact rate).
Energy (kWh) = (Watts × Hours per Day × Days) ÷ 1,000
Cost = Energy (kWh) × Price per kWh
Use this for any single device (space heaters, window AC units, pool pumps, chargers, appliances) to estimate its contribution to your electric bill, or compare the running cost of two devices doing the same job.
Many devices do not draw their rated wattage all the time. A refrigerator's label may show a maximum, but the compressor cycles on and off, so the average draw is lower than the label. The same is true of thermostat-controlled devices like space heaters, air conditioners, and water heaters. For those, estimate the hours the device actually runs rather than the hours it is plugged in, or enter an average wattage from a plug-in energy monitor. A monitor that measures real consumption over a day or a week is the most reliable way to get a number for an appliance with a variable load.
If your device only lists current, multiply amps by volts to get watts. A 120 volt device drawing 10 amps is about 1,200 watts. Some labels list a maximum current that occurs only during startup, so use running current if you know it.
Hypothetical example: a window air conditioner rated 900 watts runs about 8 hours a day for 90 days, with a compressor that is on roughly 60 percent of the time. Effective hours are 8 x 0.6 = 4.8 hours. Energy = 900 x 4.8 x 90 / 1,000 = 388.8 kWh. At $0.16 per kWh, the cost is about $62.21 for the season.
To compare an old and a new appliance, calculate the annual cost of each with the same usage and rate, then subtract. The difference is the yearly saving. Dividing the price difference of the new unit by the annual saving gives a rough payback time. This ignores rate changes, repair costs, and the value of features, so use it as one input to the decision.
Look at your bill for the price per kWh. Some bills show a supply charge and a delivery charge separately, and it is best to add them together for a total rate per kWh. Some utilities also use tiered or time-of-use rates, where power costs more at peak times or above a usage threshold. In that case the average rate on your bill is a reasonable approximation, but the actual cost of a device used at peak times may be higher. Check with your utility for current rate schedules.
The tool multiplies a constant power by time. It does not model changing loads, seasonal use, or the extra heat or cooling a device causes in a home. Treat the result as a solid approximation for planning, and confirm significant items with a monitor or your utility's usage data.
Check the label on the device itself, its spec sheet, or box -- some devices list amps and volts instead of watts directly (watts = amps × volts for that case).
No -- this calculates active-use cost only. Many electronics draw a small amount of "phantom" power even when off or in standby, which this tool doesn't estimate separately.
Use a plug-in energy monitor for a day or two, or use the annual kWh figure on its energy label, if it has one, multiplied by your rate.
Use the rate that applies when the device runs, or split the usage into peak and off-peak runs and add the results.
Bills include fixed charges, taxes, and devices you may not have counted, including standby loads.
Multiply kilowatts by 1,000 first, since the tool expects watts.