How to Calculate Appliance Electricity Costs
Learn how to convert appliance wattage and usage time into kilowatt-hours and estimate hourly, daily, monthly, and annual electricity costs.
In this guide
- Find an appliance's wattage
- Convert watts into kilowatt-hours
- Calculate hourly and monthly cost
- Account for cycling and usage frequency
- Avoid common unit mistakes
- Choose the correct DataWisdom calculator
Appliance electricity cost is calculated by converting watts to kilowatts, multiplying by operating time to find kilowatt-hours, and multiplying energy use by the electricity rate.
Information you need
To accurately calculate how much an appliance costs to run, you must gather a few specific pieces of information. Missing any of these variables will lead to incorrect estimates.
- Appliance wattage: The power the device draws.
- Runtime: How long the device operates.
- Usage frequency: How often you use it per day or month.
- Electricity rate: Your utility's charge per kilowatt-hour (kWh).
- Duty cycle: (For appliances that cycle on and off, like refrigerators).
Find the appliance wattage
Every electrical appliance has a wattage rating. You can usually find this on a silver or black product label stamped on the bottom or back of the device. If it isn't on the device, check the owner's manual or the manufacturer's online specifications.
If the label only lists Volts (V) and Amps (A), you can calculate the maximum wattage by multiplying them together: Watts = Volts × Amps. For the most accurate reading, use a plug-in energy monitor to see the actual average watts rather than the maximum rated watts.
Calculate energy use
Utility companies bill you based on kilowatt-hours (kWh), not watts. A kilowatt is simply 1,000 watts. To find the energy used, you must first convert the wattage to kilowatts, and then multiply by the hours the appliance runs.
Definitions
- Watts: The power drawn by the appliance.
- Runtime: The active operating time in hours.
Example
A 1,500W heater running for 2 hours consumes 3 kWh (1,500 ÷ 1,000 = 1.5 kW; 1.5 kW × 2 hours = 3 kWh).
Calculate operating cost
Once you know the energy consumed in kWh, simply multiply it by your electricity rate to find the final cost. Ensure your rate is in dollars (e.g., $0.15) rather than cents (15¢).
Definitions
- Energy in kWh: The calculated kilowatt-hours from the previous step.
- Electricity Rate: Your utility rate converted to dollars (e.g., 15 cents becomes $0.15).
Example
If the appliance used 3 kWh and your rate is $0.15/kWh, the cost is $0.45.
Worked example
Let's calculate the cost of running a 1,500-watt appliance for 2 hours every day for a 30-day month, assuming an electricity rate of $0.15/kWh.
| Step | Calculation | Result |
|---|---|---|
| Convert to kW | 1,500 W ÷ 1,000 | 1.5 kW |
| Daily Energy (kWh) | 1.5 kW × 2 hours | 3 kWh/day |
| Daily Cost | 3 kWh × $0.15 | $0.45/day |
| Monthly Cost | $0.45 × 30 days | $13.50/month |
Appliances that cycle on and off
Many major appliances—such as refrigerators, air conditioners, space heaters, and electric ovens—do not draw power continuously. They use a thermostat to reach a target temperature and then turn off (or enter a low-power state) until the temperature drops.
For these devices, you must estimate a duty cycle (the percentage of time the device is actively drawing power). For example, a refrigerator might have a 30% duty cycle. To estimate its cost, you would multiply the rated wattage by 0.30 to find the average active wattage before applying the standard formulas.
Common calculation mistakes
- Failing to divide watts by 1,000: Multiplying watts directly by hours results in watt-hours, making your cost estimate 1,000 times too high.
- Entering cents as dollars: If your rate is 14 cents, you must use $0.14 in the formula. Multiplying by 14 will overestimate the cost drastically.
- Treating maximum wattage as continuous draw: As mentioned above, thermostat-controlled appliances rarely draw their maximum rated wattage continuously.
- Assuming uniform monthly usage: Air conditioners are heavily used in summer, while space heaters are used in winter. Annualizing a single month's usage will yield inaccurate yearly totals.
Limitations
For more information on our calculations, please read our Methodology and Disclaimer.