What is a kilowatt hour and the cost of electricity per kWh

Understanding kW and energy costs per kWh can help you to properly monitor your energy usage and make informed decisions about how to save on your energy bills.

1 February 2023 | British Gas

What is a kilowatt (kW) and kilowatt hour (kWh)

A kilowatt hour (kWh) measures how much energy you’re using per hour. One kW equals a thousand watts of energy. You’ll be using watts of energy on all the appliances you run including heating and lights. If it’s on it is using energy – even on standby!  

Every electrical appliance has a power rating, usually shown in watts (W) or kilowatts (kW) (1,000 W = 1kW). This is the amount of electricity the appliance needs to work.

For example, if you were to run a 1,000 watt appliance at home continuously for one hour, it would consume 1 kWh of electricity. A 500 watt appliance would need to run continuously for two hours to consume 1 kWh hour, and so on.

Some appliances have a low wattage rating like a fridge-freezer, but because they’re always on they’re always using electricity. A kettle on the other hand which has a high wattage rating uses a lot of electricity but in short bursts.

All new electrical appliances and lights come with an energy label that tells you how much energy they consume in kWh, helping consumers to choose energy efficient products.

What is the cost of electricity per kWh?

When you compare energy plan prices and tariffs, or view your energy bills with your supplier, you’ll see that the unit rate of electricity and gas is shown per kWh. Your electricity provider charges you by how much electricity and gas you use per kilowatt hour (kWh), depending on the unit price.

The more kilowatt hours (kWh) you use, the more you pay.

If you’re on a standard variable tariff with your supplier, you’re protected by the Ofgem energy price cap. From 1 January to 31 March 2024, prices were set at 28.62 pence per kWh for electricity and 7.42 pence per kWh for gas including VAT. 

The exact unit cost for your gas and electricity depends on your supplier, meter type, where you live, what tariff you’re on and how you pay. You’ll find this information on your energy bill

How to calculate a kilowatt hour (kWh)

Say you have 10 x 100-watt light bulbs, that would equal 1 kW of energy.

10 bulbs x 100 watts each = 1,000 watts or 1 kW

1 kW x 10 hours usage @ 28.62 pence per kWh cost of electricity = £2.86

You can apply the same rule to your gas too (but the unit cost will be different).

It’s that simple! When you know how much 1 kWh of energy costs and how to convert kWh into pounds and pence, you’ll be able to understand how your energy bills are worked out and why some appliances use more energy than others.

What is the average kWh usage and cost for a household?

According to Ofgem, the typical British household has 2.4 people living in it and uses 2,700 kWh of electricity and 11,500 kWh of gas in a year. This works out at 242 kWh of electricity and 1,000 kWh of gas per month.

Learn about the average kWh usage by household and cost on a standard variable tariff set by Ofgem. Your actual costs could be higher or lower than the average depending on how much you use and the unit price of your gas and electricity.

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What appliances use the most kWh and what is their typical cost?

Everything with a switch uses energy when it’s on! And some appliances use more kWh than others.

The higher the rate of power (kW) of an electrical device and the longer its used (hours), the more electricity it consumes (kWh).

According to the Energy Saving Trust, below are the biggest users of electricity in the home and how much they account for on a typical energy bill.

Biggest users of electricity by appliance type

Appliance type The % amount they account for on a typical energy bill
Wet appliances like washing machines, dishwashers, tumble dryers 14%
Cold appliances like fridges and freezers 13%
Consumer electronics like laptops, TVs, game consoles 6%
Lighting 5%
Kitchen appliances like hob, oven, kettle, and microwave 4%

The power needed to heat the water for wet appliances like washing machines and dishwashers pushes up consumption making them energy-hungry household appliances. Cold appliances like fridges and freezers need to stay on all the time, so they’re continually using electricity to maintain a constant temperature. And we’re far more reliant on consumer electronics with many being left on for long periods. Remember to turn your devices off standby!

Example costs per kWh for standard appliances

Here’s a few examples of standard home appliances with assumed energy ratings and how much they would cost to run based on Ofgem’s standard variable tariff unit cost of electricity for January to March 2024:

Appliance type Assumed energy rating Usage Cost to run
Tumble dryer 3000 watts (3 kW) x 1 hour usage @ 28.62 pence per kWh £0.86
Dishwasher 1800 watts (1.8 kW) x 1 hour usage @ 28.62 pence per kWh £0.52
Microwave 900 watts (0.9 kW) x 15 minutes usage @ 28.62 pence per kWh £0.07
Kettle 1000 watts (1 kW) x 5 minutes usage @ 28.62 pence per kWh £0.03
Laptop 200 watts (0.2 kW) x 1 hour usage @ 28.62 pence per kWh £0.06

Ways you can save kWh 

Once you know your kW from your kWh and how and when you use appliances at home, you’ll really be able to understand how typical your household energy use is and the tweaks you can make to help lower your bills.

You can start by:

  • Turning appliances off standby mode – switch them off at the plug
  • Turning off lights in rooms that are not being used
  • Using the washing machine and dishwasher on lower temperatures
  • Having showers instead of a bath
  • Only boiling as much water as you need in the kettle
  • Draught-proofing windows and doors
  • Insulating water tanks, pipes and radiators

There’s lots you can try that won’t cost a thing but could save you money off your bills.

Learn more about how to save energy at home.

Take control of your energy use with smart meters

Smart meters track your energy use in pounds and pence, so you can tell exactly what you’re spending on energy.

By allowing you to track your energy use, smart meters encourage you to make small changes to use less energy, cutting bills and your carbon emissions. It’s a win-win.

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Frequently asked questions

How many watts are there in a kilowatt (kW)?

One kilowatt (kW) is equal to 1,000 watts of power. The higher the kW of an appliance or device, the more electrical power is needed to operate it. A kilowatt = 1,000 watts (W).

What’s the difference between a kW and kWh?

Although kW and kWh are related units of measure, it’s what they measure that makes them different.

A kW measures power. i.e., the rate at which something uses electricity. The higher the kW of a device the more electrical power is needed to operate it.

A kWh measures energy, the total amount of electricity used in kilowatts per hour.

For example, if you use a low-powered electrical device such an LED TV which needs 100 watts (0.1 kW) of power to run, you can use it for ten hours before consuming 1 kWh of energy. On the other hand, if you were to charge your electric vehicle with a 22 kW car charger for one hour, you will consume 22 kWh of energy.

The equation to calculate kilowatt hours is (kW x hours = kWh).

Want to know more?

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