A guide to kWh

kWh: why do you need to care about it?

Do you ever stop and think about where your electricity comes from? Understanding how it’s measured and charged can help you reduce your energy costs or even find a better deal. The unit of energy that suppliers use is called a kilowatt-hour (kWh). The rate you’ll pay per kWh will vary by supplier. Here’s our handy guide to help you answer the question of ‘what is kWh’, and how this unit impacts your energy bill.

What is kWh?

A kilowatt-hour or kWh is a unit of measurement, referring to the use of 1,000 watts over the span of one hour. It’s used by utility companies to determine how much energy a household consumes over a certain time period and to set their electricity prices per kWh. Appliances all consume different levels of energy depending on their type and efficiency level, so your use will vary correspondingly. 

To understand what kWh is, it helps to put it into perspective a little. You can visualise how much energy a single kWh represents through the following examples: 

  • Ironing clothes for 22 minutes

  • Running one full washing machine or dishwasher cycle

  • Bringing your kettle to the boil ten times

  • Using a desktop computer for four hours

  • Watching TV for three hours

Average household use will depend how many occupants there are in the property, how much time they spend at home, and what type of appliances they use. Ofgem published Typical Domestic Consumption Values in 2017 to use as a general reference. These are used as an industry standard to showcase how much gas and electricity the typical domestic consumer uses every year. 

At the lower end of this chart, a small home occupied by one or two people would use approximately 1,900 kWhs of electricity per year, along with 8,000 kWhs of gas. At the upper end of the spectrum, a large family uses closer to 4,600 kWhs of electricity and 17,000 kWhs of gas per year. Right in the middle, a medium-sized home would use approximately 3,100 kWhs of electricity and 12,000 kWhs of gas. 

These are just rough estimates, however, as every household is different. It does give you some idea of where your own household might fit in, which is helpful if you’re comparing energy rates. 

Is there a difference between a kW and a kWh?

When you’re looking at this measurement unit, you’ll see both kW and kWh mentioned. The difference is that kW refers solely to kilowatts, or the unit of power a device needs to operate at any point in time. A kWh is the unit of energy used to represent how much energy is actually used. A popular way to look at this is to think of the electrical device as a car. In this analogy, kW would refer to the speed you’re driving at (for example, 40 mph), while the kWh would indicate the distance you’ve already driven (for example, 30 miles). The more miles you cover, the more you’ll pay in fuel costs – just as your energy bill will be higher the more kilowatt-hours you use. 

For example. if your dishwasher has a power rating of one kW and you run it for one hour, it requires one kWh of energy. Another example would be a 100-watt light bulb – if you use it for 10 hours, that would add up to one kWh. 

How do I convert kW to kWh?

Knowing an electrical device’s power rating can help you stick to a budget, along with the electricity prices per kWh. These figures will give you some indication of how much energy you’re using. All appliances come with a designated power rating. While this is often clearly labelled right on the appliance or packaging, in some cases you’ll need to look at the manufacturer’s website or online product listing. 

The power rating is usually given in watts, which you’ll need to convert to a kilowatt unit by dividing the wattage by 1,000. For example, an appliance with a 500 W power rating would have a kW rating of 0.5. To convert this kW number to KWh, simply multiply the kW rating by the length of time it’s used. In the example of the appliance with a 0.5 kW rating, if you run it for 24 hours, it would use 12 kWh per day, or 0.5 kW per hour. 

Why do you need to know this? Because then you’re able to calculate just how much money you’re spending, using electricity prices per kWh. In the above case of a device that operates with 12 kWh per day, if your electricity price per kWh is 10p you would be spending £1.20 per day just on this appliance alone – or £36 per month. By shutting it off for even eight hours while you’re at work, you’ll save £12 per month!

What is the average kWh cost?

As you’ll quickly find when comparing energy prices, there’s no standard price for electricity within the UK. Suppliers are free to set their own prices dependent on market rates and additional factors. The kWh cost will vary depending on your postcode and tariff. To find the best rate, you’ll want to shop around using a comparison website. It’s still helpful to keep the average prices in mind to see how your household compares. 

The Energy Saving Trust calculates energy prices using a national average kWh cost of 13.86p per kilowatt-hour. While this is an average amount you might expect to pay, keep in mind that this applies to electricity rather than gas. Your actual rates will depend on your region, the plan you’re on, and the type of payment you use. Some customers are also on savings plans dependent on the time of day you consume energy, like Economy 7 tariffs. These offer a separate kWh price for energy used during the daylight hours and energy consumed overnight. If you’re not sure what you’re paying, this information should be clearly displayed on your energy bill. 

Why should I know my kWh usage? 

It’s clear to see why it might be worth keeping track of your kWh usage. Although it’s often skimmed over when you’re reading your utility bill, this bit of information is one of the most useful pieces of data. This is particularly true if you want to gain control of your household energy use, as you can see just how much energy you’re using, and what you’re paying for it. 

When a bill is higher than expected, take a look at your kWh electricity and gas usage to find out which appliances are using more energy. These are the areas you can then focus on to boost efficiency and slash bills. It’s a handy reminder to do simple things like turn off lights when you leave the room and wait to run the dishwasher until it holds a full load. Even the little things add up – a mobile phone left charging overnight, or a desktop computer left on standby mode when not in use. 

How can I find my kWh energy information?

Energy bills contain far more information than a simple statement of what you owe. Whether you’re pulling up a monthly bill or annual statement, be sure to have a look at the usage section. This should provide a detailed breakdown of how many kWh you’ve used during the billing period, along with the rate and your most recent meter readings. This applies to kWh electricity bills. For gas, sometimes the energy supplier will show your usage information in gas units rather than kWh energy units. If this is the case, you can use an online kWh calculator to find the correct number. 

How to switch using kWh figures 

A final reason to keep track of your kWh consumption is that it gives you ammunition for switching energy suppliers. When you visit a comparison website, you’ll be asked for some basic information, including your postcode. Having your kWh energy use information close to hand ensures that you’ll get a more accurate quote, based not just on estimations but on your real-life household figures. This means you’ll gain access to customised tariffs that best apply to your home, potentially saving more money in the process. 

Bjorn GriffithDec 9th 2019