How to calculate electricity use
kWh per day = watts × hours per day ÷ 1,000. Multiply by the days used per month for the monthly figure, and by 12 for a year. Cost = kWh × your rate per kWh. The wattage is on the appliance's label or in its manual; for devices that cycle on and off, such as refrigerators, the average use is lower than the label maximum.
Worked example: a space heater
A 1,500 W space heater running 4 hours a day uses 1,500 × 4 ÷ 1,000 = 6 kWh per day. Over 30 days that is 180 kWh; at $0.17 per kWh it costs $30.60 a month, or about $367 a year if used like that every month.
Finding your electricity rate
Your bill shows the price per kWh, sometimes split into supply and delivery charges — add them together for the calculation. Enter the rate in dollars, so 17 cents is 0.17. Time-of-use plans charge different rates at different times of day.
Typical appliance wattages
Examples of typical ranges: LED bulb 8–12 W, laptop 30–70 W, TV 50–150 W, refrigerator 100–250 W while running, microwave 1,000–1,200 W, hair dryer and space heater 1,200–1,500 W, clothes dryer 2,000–5,000 W. Check your own device for the exact figure.