Calcmeister

Electricity cost calculator

Enter the wattage of your appliance, how many hours per day you use it, and your electricity rate to estimate its energy consumption and cost. Adjust the efficiency and number of units for more accurate results.

W

Wattage of the appliance (e.g., 1500 for a space heater).

hours

Average hours the appliance runs each day.

days

Number of days per week the appliance is used.

months

Number of months per year the appliance is used (e.g., 6 for seasonal AC).

$/kWh

Your cost per kilowatt-hour (check your utility bill).

units

Number of identical appliances.

%

Appliance efficiency (100% = perfect; lower values increase energy use).

Daily energy
– kWh
Monthly energy
– kWh
Yearly energy
– kWh
Daily cost
– $
Monthly cost
– $
Yearly cost
– $

    How It Is Calculated

    This calculator estimates the energy consumption and cost of running one or more identical electrical appliances. The calculation follows these steps:

    1. Convert the power from watts to kilowatts: PkW = PW / 1000.
    2. Adjust for efficiency: Peff = PkW / (E / 100), where E is the efficiency percentage.
    3. Compute daily energy per unit: Eday,unit = Peff × H, where H is hours used per day.
    4. Total daily energy for all units: Eday = Eday,unit × N, where N is the number of units.
    5. Weekly energy: Eweek = Eday × D, where D is days used per week.
    6. Yearly energy: Eyear = Eweek × 52 × (M / 12), where M is months used per year.
    7. Monthly energy: Emonth = Eyear / M.
    8. Daily cost: Cday = Eday × R, where R is the electricity rate in $/kWh.
    9. Monthly cost: Cmonth = Emonth × R.
    10. Yearly cost: Cyear = Eyear × R.

    Eday = (PW / 1000) / (E / 100) × H × N

    Eyear = Eday × D × 52 × (M / 12)

    Cmonth = (Eyear / M) × R

    Assumptions

    Worked Example

    Suppose you have a 1000 W appliance used 4 hours per day, 7 days per week, 12 months per year, with an electricity rate of $0.12/kWh, 1 unit, and 100% efficiency.

    Practical Tips

    Questions and answers

    Why is my monthly cost different from my actual bill?

    This calculator assumes a constant electricity rate and does not include taxes, fees, or tiered pricing that may appear on your bill. It also assumes the appliance runs exactly as entered, which may not reflect real-world usage patterns.

    What does the efficiency setting mean?

    Efficiency accounts for energy lost as heat or in conversion. For example, a 1000 W appliance at 80% efficiency effectively uses 1250 W to deliver the same output. Set it to 100% for most resistive loads like heaters.

    Can I use this for appliances that cycle on and off?

    Yes, but you should estimate the average daily running hours rather than the total time the appliance is plugged in. For example, a refrigerator might run 8 hours per day even though it is always on.

    How do I find my electricity rate?

    Check your utility bill for the cost per kilowatt-hour (kWh). It is usually listed as a single rate or an average of tiered rates. If you have time-of-use rates, use the rate for the hours you run the appliance.

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    Last reviewed: 2026-10-17. Results are estimates for planning. Check them before you rely on them for design, purchase or safety decisions.