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Energy units explained - what is a kWh of electricity?

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When you look at your electricity bill or app, you’ll see the amount of electricity you’ve used is measured in kilowatt hours (kWh). Let’s explore what a kWh is so you’ve got a better understanding of how your energy usage is measured and priced.

Article Contents 

  • kWH basics explained 
    • What is a kWh?
    • What is the difference between a kW and a kWh?
  • Calculating kWhs 
    • How to calculate a kWh of electricity? 
    • What can 1 kWh power?
    • How much does 1 kWh of electricity cost?
  • kWh & electricity usage at home 
    • What is the average household usage in NI?
    • How many kWh do household appliances use?
    • How many kWh do electric vehicles use?
  • How to save kWh of electricity
    • Monitor Usage 
    • Update Appliances 
    • Energy Saving Tips 
    • Compare Tariffs 
  • FAQs 

KWH basics explained 


What is a kWh?

A kilowatt hour (kWh) is a measure used to calculate how much electricity you’re using. It helps to compare the amount of electricity different appliances use. One kilowatt hour is the amount of energy you need to run a 1,000-watt (1 kW) appliance for one hour.

  • Having a 100-watt light bulb on for 10 hours uses 1 kWh
  • Using a 2 kW dishwasher for 30 minutes uses 1 kWh
  • Running a 10 kW shower for 6 minutes uses 1 kWh 

What is the difference between a kW and a kWh?

A kilowatt (kW) measures power. Every appliance has an energy rating based on how much power it needs to run for an hour. A kilowatt hour (kWh) measures energy. It shows how much energy an appliance will consume when in use for any given period of time.

  • A 3 kW kettle would use 3 kW of power if switched on for an hour. If it boils in three minutes, it will use 0.15 kWh.
  • A 2 kW electric oven would use 2 kW if switched on for an hour. If you’re cooking for 45 minutes, it will use 1.5 kWh.
  • An 80-watt television would use 0.08 kW if switched on for an hour. Watching TV for five hours will use 0.4 kWh.

Calculating KWHs 


How to calculate a kWh? 

Understanding the amount of kWh used by different household appliances will help you to work out which energy-guzzling appliances are costing you the most money. You can then limit or change the way you’re using those appliances to cut your electricity bills.

It’s easy to work out how many kWh you’re using on individual appliances as well as your daily household kWh usage. Here’s how to do that.

  • Use an energy monitor. To work out what you’re spending on each appliance, turn off all your appliances and use an energy monitoring device or app to see your current usage in kWh. Turn on one appliance and note the increase in kWh. Repeat this for all your appliances.
  • Use simple maths. Check the watts or kW rating of any appliance on its label, packaging, manual or manufacturer’s website. Multiply the kilowatt power rating of your appliance by the amount of time it's in use. This gives the amount of kWh the appliance is using.
  • Check daily household usage. Use an energy monitor or check your bill, app or meter to see how many kWh you used over a specific period. Divide this by the number of days in that period to calculate your approximate daily usage.

What can 1 kWh power?

Since kWh helps to standardise energy usage, it’s interesting to think about the different things that 1 kWh of electricity can power. For example, 1 kWh can power your:

  • Microwave oven (800 watts) for 1 hour 15 minutes 
  • Electric oven (2 kW) for 30 minutes
  • Kettle (3 kW) for 20 minutes 
  • Air fryer (1.5 kW) for 45 minutes
  • Vacuum cleaner (1.4 kW) for 43 minutes
  • Tumble dryer (3 kW) for 20 minutes
  • Washing machine (850 watts) for 1 hour 10 minutes
  • TV (80 watts) for 12 hours 30 minutes
  • Electric heater (1.5 kW) for 40 minutes 
  • Electric fan (100 watts) for 10 hours 

How much does 1 kWh of electricity cost?

The cost of 1 kWh of electricity varies between different suppliers. It’s the standard way to show the unit price of electricity across all suppliers, plans and tariffs. That means it’s easy to check how much 1 kWh of electricity currently costs you by looking at your electricity bill or checking your supplier’s unit rates online.

If you’re a Power NI customer, you can check the current Power NI unit rates on our website.

kWh & electricity usage at home 


What is the average household usage in NI?

The Utility Regulator uses a figure of 3,200 kWh   — an average of just under 9 kWh per day — when considering average consumption. The UK Government’s latest figures show an average household electricity usage in Northern Ireland of 3,465 kW or 9.5 kW per day. The actual usage in your household will depend on how many people live in your home, what times of day you’re using electricity and how energy efficient you are.

How many kWh do household appliances use?

The amount of kWh each household appliance uses depends on its energy rating in kW and how often it’s in use. Some typical daily energy usage for common household appliances in homes in Northern Ireland include:

  • Microwave oven (based on being on for 5 minutes) - 0.66 kWh
  • Electric oven (based on being on for 45 minutes) - 1.5 kWh
  • Kettle (full kettle, based on being boiled 5 times) - 0.75 kWh
  • Air fryer (based on being on 30 minutes) - 0.75 kWh
  • Vacuum cleaner (based on being on for 10 minutes) - 0.23 kWh
  • Tumble Dryer (based on being in use for 40 minutes) - 2 kWh
  • Washing Machine (based on being in use for 40 minutes) - 0.5 kWh
  • TV (based on watching for 3 hours) - 0.24 kW
  • Electric Heater (based on being on for 2 hours) - 3 kW
  • Electric Fan (based on being on for 2 hours) - 0.2 kW 

How many kWh do electric vehicles use?

For an increasing number of households in Northern Ireland, the kWh usage of charging an electric vehicle is a new consideration. If you’re an EV owner or you’re thinking about buying an electric car, it’s easy to work out the impact on your electricity bills.

The average electric vehicle battery capacity is 40 kWh, but this varies from 20 kWh to 100 kWh depending on the make and model of the electric car. With electric vehicles, the ‘appliance’ we’re thinking about is the charger — your charging cost will be the kW energy rating of your charger multiplied by the number of hours of charging.

A full charge will give you the amount of kWh specified in your battery capacity. How quickly you use the kWh available will depend on several factors. This includes the speed at which you drive, how harshly you accelerate, the number of people or the amount of cargo inside the vehicle, and especially the distance you travel. 

  • Short Distance Journeys - The average driver in Northern Ireland travels just over 11 miles every day. If you make a 5.5-mile commute and the same home each day, that’s 3.5 kWh per day (based on an average energy consumption of 0.32 kW per mile). That works out at 110 kWh per month or 1,285 kWh per year.
  • Long Distance Journeys - Perhaps you drive further than average. If you commute from Ballymena to Belfast that’s a 56-mile round-trip. That would use 18 kWh per day, 545 kWh per month and 6,541 kWh per year.

Home charging is often the best way to maximise your miles per kWh and keep a close eye on the costs. Take a look at Power NI EV tariffs — with special rates for overnight charging — and the Power NI Mini EO charger to start charging at your home.

How to save kWh of electricity

There are lots of ways households in Northern Ireland can cut electricity consumption, reduce kWh use and lower electricity costs. Let’s explore some of the steps you can take to save kWh.

  • Monitor kWh Usage  - Use energy monitoring devices or apps to track your kWh consumption in real-time.
  • Update Old Appliances - Swap kWh-hungry old appliances for modern, energy-efficient replacements.
  • Follow Energy Saving Tips - Make simple changes to the way you use your appliances to create big savings.
  • Compare Electricity Tariffs - Switch to a plan with a lower unit rate to cut the cost of every kWh you use. You can make savings on your Power NI bills by choosing a plan that offers a lower kWh unit rate depending on the time of day you use electricity or how you want to pay.




How can you work out gas kWh?

Gas usage is usually recorded on gas meters in cubic metres. To convert cubic metres into kWh you have to multiply the units on your gas meter by something called the conversion factor. This is the amount of energy in kWh released by burning 1m3 of gas. It changes based on the calorific value of the gas, which in turn varies based on where it’s sourced, its physical composition and local temperatures.

To convert a gas meter reading into kWh, multiply your meter reading by the volume correction factor (1.02264), multiply by the calorific value and divide by the conversion factor.

What are some other measures of electricity?
We’ve discussed that watts and kilowatts measure power and the kWh measure energy. For industrial scale measuring, electricity is also measured in megawatt hours (MWh) and gigawatt hours (GWh). One megawatt (MW) is 1,000kW and one gigawatt is 1,000MW.