The best way to calculate your carbon footprint

A calculator may be needed to work out your carbon footprint!
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As climate change becomes an increasingly scary issue, it is essential we are aware of our impact on the environment. The most accessible way to do this is to calculate your carbon footprint. There are many carbon footprint calculators online and these are undoubtedly a useful tool to learn about your impact. However, it is also important to learn about how these figures are calculated. The website FootprintFacts, and the tools on it, were created out of a desire to educate and inform people in more detail about their carbon footprint. One of the best ways to learn about your impact on the environment is to calculate your footprint on your own. This article explains how to do that.

Obviously, the most accurate and easy way to calculate your carbon footprint is to use a calculator. The FootprintFacts calculator uses many of the same techniques detailed in this article. We recommend using both the calculator and this article alongside each other.

The carbon footprint of you home

Heating and power

When looking at the carbon footprint of your house, it is important to remember that it is very tricky to measure the exact impact. This is because there are so many variations on house size, design and energy usage. By far the most accurate way is to take your energy usage in kWh (kilowatt-hours) and multiply it by the amount of CO2 per kWh in your country, and for your fuel. Usually, the kWh used will be given on your electricity bill.

In the UK in 2019, for electricity the CO2 per kWh was 0.256kg, and for natural gas it was 0.184kg. Suppose you used x kWh in a month, your CO2 output would be 2.1kg.

However, most people don’t know their exact electricity usage. Because of this, it is often easier to approximate. There are several factors needed in order to approximate the carbon footprint of your house. The most important are:

1. Insulation

The level of insulation is significant since it tells us how energy efficient your house is. If your house is very insulated, it will use less energy to heat your house to the same temperature. Select the descriptor from the list below which best suits your house and note down the number.

Very 50
Fairly 100
Slightly 150
Not 250

2. Size

The size of your house is significant, since a larger house will require more energy to heat. To calculate this, at FootprintFacts, we have calculated the best way to approximate the size of your house is to take the number of rooms and multiply by 20m2. However, if you know the exact size of your house, we recommend you use this instead.

3. Fuel efficiency

Finally, you need to know the fuel you use in your house. Each fuel has a different efficiency, which is listed in the table below. If you have a renewable energy supplier, such as bulb the carbon footprint of heating your home is zero! To calculate your fuel efficiency, select one of the fuel efficiency figures from the table below. To find out more about where these approximations come from, check out this article.


Finally, to calculate the carbon footprint of your house, multiply the insulation factor by the size and the energy efficiency. For example, if I had a very insulated house which was 100m2 and heated by gas my footprint would be calculated by:

50 x 100 x 0.21 = 1050kg per year

Home Appliances

One of the first questions we asked at FootprintFacts was: “How much carbon dioxide does boiling a kettle release?” We wanted to know what the worst thing to do for the environment in the home was, and how much carbon dioxide they release exactly. In order to calculate the carbon output of home appliances we need to know 2 things.

  1. The energy the appliance uses
  2. How much carbon dioxide is released when you use energy in the home

The first part is pretty simple. All you need to do is to find the wattage of the appliance you are using (how much energy it uses per second) and the time you use it for. Take a kettle, for example. The wattage in a kettle is around 2600W and it takes about 2 minutes (120 seconds) to boil a kettle. If we use the equation:

Energy = Power x Time (in seconds)

We can calculate that the energy used to boil a kettle is about 312 kilojoules (312000 joules). 

Next, we need to find how much carbon dioxide is released for each kilojoule you use in the home. To find this we use a statistic from the government carbon emissions report, which tells us that 0.05g of carbon dioxide is released per kilojoule. 

If we multiply 0.05 x 312 we find that the carbon output of boiling a kettle is 15.6g. If you use the same method, you can calculate the carbon impact of any home appliance. We recommend either finding the wattage of your appliance on the manual it came with or the producer website.

The carbon footprint of travelling

Travel is one of the biggest sources of carbon dioxide. It’s also one of the easiest to calculate. All you need to know is two things –

  1. How far you have travelled
  2. How much carbon dioxide is released by the vehicle you have travelled in

There are several ways to calculate how far you have travelled. If you make a one-off journey, you can use to calculate the distance. If you want to approximate the distance you drive, or travel per year – calculate the approximate distance you travel per week, and multiply this figure by 56 (the number of weeks in a year).

Now you need to multiply the distance travelled by the efficiency of the vehicle. The carbon dioxide released per kilometre travelled for some of the more common vehicles is listed below: 

Small Car0.15kg
Medium Car0.18kg
Large Car0.2kg

The bus and train are a lot more efficient since they can have a lot of people onboard. This reduces the CO2 released per person.

Finally, to calculate this carbon footprint of your journey, multiply the distance (in km) by the efficiency of the vehicle. For example, if I travel 20km in a bus, my carbon footprint is calculated by:

20km x 0.09 = 1.8kg of carbon dioxide

If you use the FootprintFacts comparison tool, this calculation is done automatically.

The carbon footprint of food

Calculating the carbon footprint of your diet is often trickier, and usually requires a lot of approximation. This is because the carbon footprint for different food varies in different areas. However, we can get a pretty good idea by looking at some of the averages. If you want the full list of the carbon footprint of food – check out our comparisons tool

To calculate the annual carbon footprint of your diet, the easiest method is to track what food you eat in a typical week. You can do this by noting down the main constituents of each meal and roughly how much they weigh. At the end of the week, use the FootprintFacts comparison tool to work out the carbon footprint of each item of food you have eaten. If you add them all together and multiply by 56, you will get your yearly diet carbon footprint.


This article summarises how you can get an idea of your footprint in some of the key sectors. However, there are many other factors which contribute to your footprint. We recommend reading our other articles and completing the FootprintFacts carbon footprint calculator so that you can stay the most informed about your footprint as possible.

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