Convert appliance power into electricity cost
Electricity bills generally charge for energy, not simply a device's rated wattage. Watts describe power at a particular moment, while kilowatt-hours accumulate as equipment operates. A 1,000-watt appliance running for one hour consumes 1 kilowatt-hour under the assumption that it draws its rated power continuously. The calculator multiplies energy per hour by daily operating time, number of days and the number of identical devices.
The electric rate is entered directly, so it can reflect a tariff from a bill or a hypothetical scenario. Some utilities use tiered rates, time-of-use periods, demand charges or separate delivery fees. One rate per kilowatt-hour can approximate the energy portion of the bill, but it is not necessarily the all-in change in the monthly amount due.
Electricity usage formula
Energy (kWh) = power (kW) × operating hours per day × days × devices
Energy charge = energy (kWh) × entered price per kWh
For intermittent appliances, the actual average draw may be lower than the nameplate power. A refrigerator cycles on and off, air-conditioning compressors vary by load, and modern electronic devices may use different power levels during operation, idle and standby. A plug-in energy meter or utility interval data can provide a better input than maximum rated power when measured consumption matters.
Worked example: a 1,500-watt device
A 1,500-watt heater draws 1.5 kilowatts while operating. At 3 hours per day for 30 days, the calculation is 1.5 × 3 × 30 = 135 kilowatt-hours. If the user enters an illustrative electricity rate of $0.18 per kilowatt-hour, the energy charge is 135 × $0.18 = $24.30.
That calculation assumes full-rated power for all 90 operating hours. A thermostat that cycles the heater off would reduce energy use, while taxes and fixed utility fees may increase the total bill.
Estimating appliances that do not run continuously
The simplest improvement is to estimate equivalent full-load hours rather than wall-clock hours. If a 2,000-watt appliance runs at rated power for approximately half of a ten-hour period, five full-load hours is an appropriate arithmetic input. For variable-speed equipment, use measured average wattage when available. Avoid mixing a nameplate maximum with hours derived from a lower-power operating mode.
When comparing equipment, calculate consumption under the same hours, rate and operating assumptions. A lower-watt appliance may still use more energy if it runs longer. Energy use is the more useful comparison because it incorporates both power and time.
Electricity cost questions
What is the difference between kW and kWh?
A kilowatt measures power. A kilowatt-hour measures energy consumed when one kilowatt is used for one hour. Utility energy charges are typically based on kilowatt-hours, not kilowatts alone.
Does this calculate my complete electricity bill?
No. It calculates a variable energy charge using one entered price per kilowatt-hour. Standing charges, taxes, demand fees, seasonal tariffs and different time-of-use prices are not modeled and may change the amount shown on the actual bill.
Why is measured wattage better than the label rating?
A label may state maximum demand, while normal operation cycles between power levels. Measured average consumption or a representative power value usually gives a better estimate for equipment with variable load or standby behavior.