Gas and electricity meter in a garden

A guide to kWh

The Kilowatt-hour is unit used by energy companies to determine how much you are charged, understanding what it represents can help you to reduce your energy bills.

What is a Kilowatt-hour?

A Kilowatt-hour or kWh is defined as the amount of energy used by a 1,000 Watt appliance over the course of an hour, for example: A 1,000 Watt electric heater left running for one hour uses 1 kWh of energy.

kWh is the standard unit of measurement used by energy suppliers for both electricity and gas .

What is a Kilowatt?

A kW is a measurement of power equal to 1,000 Watts, it describes how much power is needed by an appliance to work, it differs from a kWh in that the energy used by an appliance over a given period of time cannot be described in Kilowatts.

Put simply, Kilowatts describe how much energy an appliance is using at any given moment, a Kilowatt-hour describes how much energy it has used over a period of time.

To give an example, a 100 Watt bulb being left turned on for 10 hours uses 1 kWh of energy or the same amount as a 1,000 Watt (1 KW) microwave being used for 1 hour.

An easy way of understanding kW and kWh is to think of kW as how quickly water flows from a tap and to think of kWh as how much water is in the sink.

How do Kilowatt-hours apply to energy from gas?

Energy companies buy gas by it’s volume which is measured in cubic metres but one cubic metre of gas does not always produce the same amount of energy when it is burnt.

The amount of energy produced by gas when burnt depends on a number of factors including the calorific value of the gas, these are all calculated by your energy company before you receive your bill which will just be presented as a price for a certain number of kWh.

So what does 1 kWh power represent?

Different consumer products use varying levels of energy, but to give you an idea one kWh can do the following:

  • Light a 40W bulb for 25 hours.
  • Power an iron for an hour.
  • Boil a full kettle 10 times.
  • Power your laptop for 2 days.

How much does a Kilowatt of energy cost?

Costs per unit depend on a variety of factors including what type of energy tariff you are currently on, which energy supplier you are with and in some cases what time you consumed the energy, for example those who might be on a night saver tariff.