Your electricity bill measures your consumption in kilowatt-hours (kWh). Yet your appliances - such as your toaster, microwave, or fridge - indicate power ratings in kilowatts (kW). What is the difference between the two? Our guide will help explain so that you can better understand your electricity consumption.
What is a Kilowatt?
A kilowatt is a measure of power. Power is the rate at which energy is converted from one form to another; it measures how quickly energy is being used. This relationship is clearer when power is measured in terms of Joules (a unit of energy) per second. In fact, a watt is another name for Joules/second.
If energy were to be compared to distance, then power would be the measure of speed. i.e. just like speed is the distance travelled over a certain amount of time, power is the amount of energy consumed (or produced) over a certain amount of time.
However, a watt (J/s) is a small unit for measuring power, especially when we are talking about consumption at large scales (think about how much power a house, a city, or a country consumes). This is why we use kilowatts (kW). A kW = 1000 watts). One kilowatt is roughly equivalent to 1.34 horsepower.
A kilowatt therefore refers to the rate at which electrical energy can be used or generated. For an appliance, kW refers to the rate at which electricity is used to run the appliance. For example, a microwave that has a wattage of 1 kW uses 1000 watts (1 kW) when it is running. When it isn’t running, it uses no power (or next to no power). Similarly, a blender might have capacity to use 0.7kW (700 watts) when it runs, but doesn’t use power when it is not running (you could also think of the blender as using 700 Joules/second). So in other words, we know that a blender has the capacity to use 0.7kW when it is running, but this doesn’t tell us how much energy it has actually used.
This is where the kilowatt-hour comes in.
What is a Kilowatt-Hour?
A kilowatt hour (kWh) is a measure of energy, like the Joule, a calorie, or British Thermal Unit (BTU). When you buy electricity, your utility company charges you by the kilowatt-hour (kWh).
A kWh measures the amount of energy equivalent to using one kilowatt over one hour. For example, if you ran your 1 kW microwave for one hour, you would use 1 kWh of energy. If you used your 0.7 kW blender for one hour, you would use 0.7 kWh of energy.
Consumption per appliance can vary from 60 watts (0.06 kilowatts) for a lightbulb, to 15,000 watts (15 kilowatts) for central air conditioning.
If you use a 15 kilowatt central air system for 2 hours, your consumption amounts to:
15 kilowatts x 2 hours = 30 kilowatt-hours (kWh)
How much energy do my appliances use?
|Appliance||Typical Watts per appliance||In Kilowatts|
|Central Air Conditioning||15,000 watts||15 kilowatts|
|Clothes Dryer||4,000 watts||4 kilowatts|
|Coffee Maker||1,000 watts||1 kilowatt|
|Desktop computer (monitor included)||400 watts||0.4 kilowatts|
|Electric stove burner||1,000 watts||1 kilowatt|
|Hair Dryer||1,200 watts||1.2 kilowatts|
|Heat Pump||15,000 watts||15 kilowatts|
|Light bulb (60-W incandescent)||60 watts||0.06 kilowatts|
|Refrigerator||1,000 watts||1 kilowatt|
|Space heater||1,500 watts||1.5 kilowatts|
|Television||97 watts||0.097 kilowatts|
|Vacuum cleaner||542 watts||0.542 kilowatts|
|Water heater||4,000 watts||4 kilowatts|
|Water Pump||3,000 watts||3 kilowatts|
The above figures reflect active use of your appliance. Many appliances still consume energy when they are plugged in but not in use. For example, the average television consumes 97 watts (0.097 kilowatts) when it is turned on, and 4 watts (0.004 kilowatts) when it is turned off but still plugged in. Check out our article on vampire energy for more information.
Finding Your Appliance's Consumption
Most new appliances will have their maximum consumption printed on the back or the bottom. Consumption varies based on whether the appliance is in use, and what setting the appliance is used on. For example, a fan on a higher setting will consume more kilowatt-hours than a fan on a lower speed.