Between watts, watt hours, energy, and power, it can become confusing to work out what each term means. Although watts and watt-hours are related terms, they are not the same thing. In this article, we’ll help you understand the difference.

What is a watt?

A watt is a unit of power. It is the amount of energy an item needs to function; the rate at which energy is consumed. One watt is equivalent to electricity flowing at a rate of one joule (unit of energy) per second. The symbol for a watt is ‘W’.

What is power?

Power is the rate at which energy is either produced or consumed; the rate at which energy flows. Power is measured in watts.

What is energy?

Energy is the capacity to do work – such as creating light, heat, or motion.

What is a watt-hour?

A watt-hour is a unit of energy. It is the amount of energy an item consumes over a given timeframe; a way to measure the amount of work generated or performed. Watt hours are generally measured in kilowatt-hours. The symbol for watt-hours is ‘Wh’.

What’s the difference between watts and watt-hours?

Watts measure power; and watt-hours measure energy

A helpful analogy

You can think of watts and watt-hours as speed and distance.

Speed = how fast you drive at an instant in time (like a how much power is used at an instant in time; a watt).

Distance = the length, or amount that you drive over a period of time (like how long energy is used for; a watt-hour).

What is a kilowatt-hour?

A kilowatt-hour is a measure of electrical energy equivalent to a power consumption of one thousand watts for one hour. I.e. 1 kWh = 1000 Wh The symbol for kilowatt-hours is ‘kWh’.

What is a megawatt?

A megawatt (MW) is one million watts. This measure of energy is used for high energy consumers such as: large electric motors aircraft carriers Submarines server farms data centres scientific research equipment

Variations on kilowatt hours

1 kilowatt hour (kWh) = 1,000 watt hours (Wh)

1 megawatt hour (MWh) = 1,000 kilowatt hours (kWh)

1 gigawatt hour (GWh) = 1,000 megawatt hours (MWh)

An example

A 60-watt lightbulb will consume electricity at a rate of 60 watts. If you keep this light on for an hour, you will have used 60 watt-hours – 0.06 kilowatt-hours. (Remember, 1000 watts = 1 kilowatt.) This means that it takes 0.06 kWh of energy to run a lightbulb for an hour. The more powerful an appliance, the higher the watts.

How do I know an appliance’s wattage?

Information about an appliance’s energy needs appears on its technical description.

What unit do I see on my electricity bill?

Electricity suppliers measure the electricity you’ve used in a given time period (usually a month) in kilowatt -hours (kWh). How are energy costs calculated? Your supplier will charge you a unit cost per kilowatt-hour. They will take the amount of kWh used in a month multiplied by the unit cost to give you your energy consumption costs for that month. This unit charge can change according to demand and other charges.

Where did the watt get its name?

The watt is named after a Scottish inventor named James Watt, inventor of the steam engine. The name for a unit of energy was initially proposed by C. William Siemens in August 1882 in his President’s Address to the Fifty-Second Congress of the British Association for the Advancement of Science. He proposed that Watt would be an appropriate name for a unit of power.

Knowing the difference between watts and watt-hours can help you better understand your electricity bill and energy consumption.