Electricity Cost Calculator
Estimate how much any appliance costs to run daily, monthly, or annually based on its wattage, hours of use, and your utility rate. Ideal for budgeting energy costs or comparing efficient replacements.
Last updated: September 2026
Formula below · 2 sources (nfpa.org, Wikipedia) · Updated Sep 2026
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About this calculator
Electrical energy consumption is measured in kilowatt-hours (kWh), calculated by multiplying power in kilowatts by hours of operation. The annual cost formula is: Annual Cost = (watts / 1000) × hours_per_day × rate_per_kWh × 365 / efficiency_factor. Dividing watts by 1,000 converts to kilowatts, and multiplying by daily hours and 365 gives annual kWh. Multiplying by the utility rate ($/kWh) converts energy to dollars. Most nameplate wattages are the electrical power the device draws from the wall, and in that case efficiency does not change the bill: leave the factor at 100%. Use a lower factor only when the wattage you entered is the device’s useful output, such as a motor’s shaft power (1 hp = 746 W), so that the electrical input = output ÷ efficiency. The U.S. average residential electricity rate is about $0.16/kWh (2024), but rates vary widely by region and time-of-use tariff.
How to use
Say you want to find the annual cost of a 1,500-watt space heater used 4 hours per day at $0.15/kWh with an efficiency factor of 1.0. Step 1: convert watts — 1,500 / 1,000 = 1.5 kW. Step 2: multiply by daily hours — 1.5 × 4 = 6 kWh/day. Step 3: multiply by 365 — 6 × 365 = 2,190 kWh/year. Step 4: divide by efficiency — 2,190 / 1.0 = 2,190 kWh. Step 5: multiply by rate — 2,190 × $0.15 = $328.50/year. That same heater run only 2 hours/day would cost roughly $164.25 annually.
Frequently asked questions
How do I find the wattage of my appliance to calculate electricity cost?
Most appliances have a nameplate label on the back or bottom listing wattage, voltage, and amperage. If only amps and volts are listed, multiply them together to get watts (W = V × A). For variable-load devices like refrigerators or air conditioners, use the rated running wattage, not the startup surge. Manufacturer specification sheets and energy guides also list average annual kWh consumption directly, which you can use as a shortcut.
What is a good electricity rate to use in the calculator if I don't know mine?
The U.S. national average residential electricity rate is approximately $0.16 per kWh as of 2024, but it ranges from about $0.10/kWh in states like Louisiana to over $0.30/kWh in Hawaii and parts of California. Find your exact rate on your monthly utility bill — look for 'rate per kWh' or divide your total charges by total kWh used. If you have a time-of-use plan, use the rate that applies during the hours the appliance typically runs.
What does the efficiency factor mean in an electricity cost calculation?
Most appliances list the electrical power they draw, and that is what your meter bills, so the efficiency factor should stay at 100%. The factor is only for wattages that describe useful output, such as a motor rated in shaft horsepower: a motor delivering 746 W (1 hp) at 85% efficiency draws 746 / 0.85 = 878 W from the wall. Do not enter heat-pump COP here; for a heat pump, enter the electrical input power from its nameplate or spec sheet instead.