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How we calculate your carbon footprint

Our carbon calculator asks you questions about your day-to-day life, like how often you drive, eat meat, or buy new gadgets. It then crunches those numbers to come up with a single number: your carbon footprint.

We've tried to keep it simple, so you can start making changes to your lifestyle and reducing your carbon footprint right away. Because of this, your result is an estimate.

That said, our squirrels have used some heavy-duty maths to work out the carbon emissions of every product or activity. And as any good maths teacher knows, it’s vital that you show your workings. Ours are below and have been reviewed by independent researchers from Imperial College London.

How we calculate travel emissions

Land travel

We multiply the amount of time you spend using different types of transport by their average speed to work out how many miles you travelled. We then multiply that by the relevant 2019 UK government emissions factors for the underground, train, bus, motorbike, and different types of cars, including petrol, diesel, plug-in hybrid, hybrid or electric vehicle.

An emissions factor tells you how much CO2e is created per unit of activity. For example, taking the train emits 0.0662kg of CO2e per mile. Multiplying that by how many miles you travelled will give you the carbon footprint of that journey.

To keep the calculator easy to use, we use some UK average emissions factors to calculate your land travel. We use the emissions factor for average sized UK cars and motorbikes, rather than using small, medium or large vehicle types. We use the emissions factor for average UK local bus emissions, rather than specifically London or non-London buses. We use the emissions factor for national, rather than international, trains.

Air travel

We multiply the amount of time you spend flying by the average speed of a plane (900km/hr) to work out the distance you travelled. If you select a 4-8 hour journey, we use a 6 hour median. If you select a 8-12 hour journey, we use a 10 hour median, and so on. We then multiply that by the 2019 UK Government emissions factor to give the carbon footprint for that flight.

We’ve used emissions factors which include the effect of radiative forcing, which is the difference between the sunlight that is absorbed by the Earth and that which is radiated back into space. Climate scientists are generally agreed that radiative forcing should be taken into account when calculating the total climate impact of flying. 

To keep the calculator easy to use, we assume that you fly in economy class. However, a World Bank report found that flying by business or first class increases the carbon footprint of your journey, because fewer people fit into those cabins.

How we calculate food emissions

A recent University of Oxford study detailed how much CO2e is produced by different food types. Meat, dairy and eggs are the most carbon-intensive food groups, because they involve the rearing and transportation of animals.

The study calculates the kgCO2e per serving of each type of food. We multiply that by how often you eat them. For example, a 75g serving of beef produces 7.73 kg CO2e. If you eat beef once a week, that results in 0.4 tonnes of CO2e from your beef consumption each year.

We give everyone the minimum emissions of a vegan diet (see how we calculate 'baseline' emissions below), then add the emissions of animal products, depending on how often you eat them.

Why we ask about the things you buy

Everything we buy has 'life cycle emissions'. These are the emissions that occur throughout a product's life, from sourcing materials, to manufacture, to transportation and use.

The organisation Carbon Footprint provides data on how many tonnes of CO2e are produced per £1 spent on different things you can buy. We've multiplied this by the amount of money you spend on clothes and shoes, toiletries and health products, electronics and technology, and furniture and household appliances.

How we calculate your home energy emissions

If you're with Bulb, then you can rest easy. We supply 100% renewable electricity and 100% carbon neutral gas to our members. So your annual CO2 emissions with us are zero.

If you told us you use renewable electricity and 100% carbon neutral gas at home, then we've not added any carbon emissions.

If you're not with a renewable supplier, or you're not sure, then we use Ofgem data for average energy usage per UK home, which is 2,900 kWh electricity and 12,000 kWh gas each year. We multiply this by the 2019 UK government emissions factors for the UK average fuel mix.

We add a 'baseline' to everyone's footprint

These are the emissions you have little direct control over, for example your share of government services and the production and distribution of food. It also includes emissions from your household waste and your water usage based on UK averages. 

We wanted to keep the calculator simple. So rather than ask about every little thing you do, we estimated them using the calculations below.

Living in the UK

Carbon Independent calculate that each person living in the UK is responsible for 1.1 tonnes of CO2e emissions over which they have no direct control. This is down to national services like the NHS, armed forces, social services and schooling.

You may not be able to make changes to this directly, but you can take action. For instance, joining a campaign or speaking to your local MP to push for national services to switch to renewable energy or be more energy efficient.

Food

Carbon Independent estimates each person in the UK is responsible for 0.18 tonnes per year of food emissions they can't avoid. This is down to things like methane emissions from soil management, and carbon emissions from farming and operation of retail stores.

We give everyone the minimum emissions of a vegan diet, which is 0.25 tonnes of CO2e per year according to a recent University of Oxford study. We also use this data for the questions about what food you eat.

Waste

The average UK home produces 0.975 tonnes waste each, according to UK statistics on waste. DEFRA statistics suggest the average home recycles 45% of that. We multiply the amount of waste that's recycled, and the amount that's sent to landfill, by the relevant 2019 UK government emissions factors. We then divide this by the number of people living in your home to make it an individual footprint.

Water

The Energy Savings Trust estimates the average UK home uses 349 litres of water each day. We multiply this by the 2019 UK government emissions factors to work out the emissions from water usage in the average UK home. We divide this by the number of people living in your home to make it an individual footprint.