Appliance Energy Cost Calculator
Calculate exactly how much an appliance costs to run per month and per year based on its wattage, usage schedule, and your local electricity rate. Ideal for comparing appliances or spotting energy hogs.
About this calculator
Electricity cost is determined by how much power an appliance consumes and how long it runs. The formula is: Monthly Cost = (wattage / 1000) × hoursPerDay × daysPerMonth × electricityRate / efficiency. Dividing wattage by 1,000 converts watts to kilowatt-hours (kWh), the unit utilities bill. Multiplying by daily hours and days per month gives total kWh consumed. Multiplying by the electricity rate ($/kWh) converts energy to dollars. The efficiency divisor (0 < efficiency ≤ 1) adjusts for appliances that don't convert all drawn power into useful output—for example, an older refrigerator motor running at 85 % efficiency has an efficiency factor of 0.85, so its effective energy cost is higher. Multiply the monthly result by 12 for an annual figure.
How to use
You want to find the monthly cost of running a 1,500 W space heater for 6 hours/day over 30 days, with an electricity rate of $0.13/kWh and an efficiency of 1.0 (electric resistance heaters are essentially 100 % efficient). Step 1 — kWh/day: 1500 / 1000 × 6 = 9 kWh. Step 2 — kWh/month: 9 × 30 = 270 kWh. Step 3 — monthly cost: 270 × $0.13 / 1.0 = $35.10. Multiply by 12 to get an annual cost of $421.20. If you reduced daily use to 4 hours, the monthly cost drops to $23.40.
Frequently asked questions
How do I find the wattage of my appliance if it's not labeled?
Most appliances have a nameplate on the back or bottom listing watts or amps and volts. If only amps and volts are shown, multiply them: Watts = Amps × Volts (e.g., 10 A × 120 V = 1,200 W). For appliances with variable power (like microwaves or inverter air conditioners), use the maximum rated wattage for a conservative estimate. A plug-in energy monitor such as the Kill A Watt meter gives a real-world measurement averaged over actual usage patterns, which is often more accurate than the nameplate figure.
What is a typical electricity rate per kWh in the United States?
As of 2024, the U.S. average residential electricity rate is approximately $0.16 per kWh, but rates vary widely by state and utility. Hawaii has the highest rates at roughly $0.38/kWh, while states like Louisiana and Washington sit near $0.10–$0.11/kWh. Your exact rate appears on your monthly electricity bill—look for the 'Energy Charge' or 'Rate per kWh' line. Many utilities also apply tiered pricing, time-of-use rates, and fixed charges, so your effective per-kWh cost may differ from the base rate. Using your actual blended rate (total bill ÷ total kWh used) gives the most accurate cost estimate.
Why does appliance efficiency affect electricity cost calculations?
Appliance efficiency describes what fraction of the electricity drawn from the wall is converted into useful work—heating, cooling, light, or mechanical energy. An appliance with 90 % efficiency (0.9) wastes 10 % of drawn power as heat or other losses, meaning it must run longer or draw more power to deliver the same result. In the formula, dividing by efficiency scales the cost upward to reflect this waste. For electric resistance heaters, efficiency is effectively 1.0; for older refrigerators or motors it may be 0.75–0.90; for incandescent bulbs it can be as low as 0.05 since 95 % of power becomes heat rather than light.