THE NUMORIX GUIDE
How to use the Electricity Cost Calculator
Last reviewed September 12, 2026
What this electricity cost calculator does
This calculator estimates the energy cost of an appliance or device from its wattage, hours used per day, and electricity rate. It converts watts to kilowatts, calculates energy in kilowatt-hours, and scales the result to a day, month, or year where supported.
Electricity cost formula
Energy used in kilowatt-hours = watts / 1000 x hours. Estimated cost = kilowatt-hours x rate per kilowatt-hour. If an appliance uses 1,500 watts for four hours, it uses 1.5 x 4 = 6 kWh before the electricity rate is applied.
Worked example
At a rate of $0.18 per kWh, a 1,500-watt appliance used for four hours costs about 6 x $0.18 = $1.08 for that day. Used every day for 30 days, the same assumption produces about $32.40 before fixed charges and taxes.
How to interpret the result
The result estimates the variable energy portion of use. A device may cycle rather than run at its rated wattage continuously. Your bill may also include delivery fees, fixed charges, taxes, time-of-use rates, and tiered pricing. For a better estimate, compare the modeled daily kWh with the usage history on the utility bill and adjust for seasonal operation.
Common mistakes to avoid
Divide watts by 1,000 before multiplying by hours. Use the actual electricity rate from the bill rather than a national average when possible. Separate daily usage from the number of days in the billing period.
Assumptions and limitations
The calculator assumes the entered wattage and hours represent average use. It does not measure cycling behavior, standby power, seasonal rate changes, demand charges, or utility-specific billing rules. A plug-in meter can reveal actual average draw for devices whose rated wattage is only a maximum.