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Enter your device usage and electricity rate, then calculate to see the cost and energy breakdown.
How It Works
This calculator determines your energy costs using standard electrical formulas. It converts wattage to kilowatts, calculates the total hours of use, and applies your electricity rate.
Monthly Energy (kWh)
Monthly Cost
Daily Cost
Annual Cost
- Watt (W): The standard unit of power indicating how much energy a device uses at a specific moment.
- Kilowatt (kW): Equal to 1,000 watts.
- Kilowatt-hour (kWh): A unit of energy equal to running a 1,000-watt appliance for one hour. This is how utilities bill you.
- Electricity rate: The price your utility company charges for one kilowatt-hour of electricity.
Worked Example
- Monthly energy: 90 kWh
- Monthly cost: $16.20
- Daily cost: $0.54
- Annual cost: $194.40
Note: This is an illustrative example. Your actual cost will depend on your specific device and utility rates.
Assumptions
- Wattage represents the average operating power of the device.
- Usage is assumed to be consistent across the selected days and months.
- The electricity rate is treated as a flat, continuous rate.
- Results exclude unrelated household energy consumption.
Limitations
- Many appliances (like refrigerators or heaters) cycle on and off via thermostats, so they don't draw maximum power continuously.
- Time-of-use pricing and tiered utility rates may alter your actual cost based on when you use the device.
- Taxes, fixed connection fees, and seasonal utility adjustments are not included in the calculation.
- Measured wattage in real-world conditions often differs from the rated wattage printed on the device label.
Improve the Accuracy of Your Estimate
- Use measured wattage: Instead of relying on the manufacturer's maximum rated wattage, plug your device into an inexpensive electricity usage monitor to see its actual continuous draw.
- Use the effective electricity rate: Rather than using the advertised supply rate, calculate your "effective rate" by dividing your total electric bill amount by your total kWh used. This bakes in taxes and variable delivery fees.
- Account for cycling: If calculating for a refrigerator or air conditioner, remember that the compressor may only run 30% to 50% of the time. Estimate the actual "active" hours rather than the total hours it remains plugged in.
- Recalculate seasonally: If your utility charges different rates in summer versus winter, run separate calculations to understand your cost variations.
Sources and Methodology
Our calculator applies standard electrical engineering formulas (Watts to Kilowatts to Kilowatt-hours) to determine energy consumption and cost.
For more details on how we build and verify our tools, please see our Methodology page. We consult authoritative references such as the U.S. Department of Energy and U.S. Energy Information Administration for baseline energy consumption averages and national electricity rate benchmarks. These references are used to validate the mathematical structure of our tools; the actual calculated output depends entirely on the data you enter.