CO2 calculator

CO2 calculator
IPCC report of 2018: halve global emissions by 2030
Key messages from Greta Thunberg and the other youth activists
Climate crisis 10-point action plan Planting trees is not the answer Reduce your carbon footprint: 10% per year
Emissions from home energy Emissions from cars Emissions from food Buses Aviation
The "Net Zero 2050" UK Government deceits UK Government deceit: overclaiming the reduction in UK CO2 emissions
Basic UK energy and greenhouse gas statistics UK average footprint
About us

The climate crisis and what to do about it

Key points Climate change: the basics Stop burning fossil fuels: Stay within the budget of 420Gt CO2 Global emissions are rising and governments are failing The rising feeling of desperation Simple solutions for the climate crisis, which should have been implemented already

Action needed

Summary Local government Local government: Make walking safe National government Organisations Individuals Passivhaus home standards 'Offsetting'?

False and dubious solutions

Tree planting claims by Zurich scientists were withdrawn "Hydrogen power"

Awareness raising

Leaflets, video

Civil disobedience

Civil disobedience in a democracy: Q and A Civil disobedience and the law Extinction Rebellion

Reasons for optimism

Decline in UK domestic aviation Decline of domestic aviation in Sweden

Tecnicalities by sector

The UK has not cut its greenhouse gas emissions International comparisons "Green electricity" Health, education, etc emissions Trains Calculator version information

Standards of administration in a democracy

Effective planning Nolan's Seven Principles of Public Life

Performance assessments

Assessing performance on the climate crisis BEIS is not telling the truth on carbon emissions Transport for the North: Failing on the climate crisis Steve Rotheram: failing on the climate crisis

Best practice examples

Wirral Council's emission reduction trajectory Why trust this website?





Emissions from cars


The calculator uses a factor of 14.3 kg CO2 per gallon of fuel.
Carbon dioxide arises from


CO2 from fuel use:
The CO2 emissions from petrol and diesel are around 2.4 kg per litre [1], i.e. 10.9 kg per gallon (since 1 gallon is 4.546 litres).

Energy used in oil extraction:
The CO2 generated per person in oil extraction together with gas extraction is estimated as 0.28 tonnes per year (from source [2], chart A). Since oil use and gas use are roughly equal in the UK in energy terms, we can allocate half (0.14 tonnes per year) to each of oil and gas.

Energy used in oil refining:
This is estimated as 0.43 tonnes per person per year (source [2], Chart A, "Refining industries").

Construction of cars and their maintenance:
From a financial point of view, fuel costs are just a small part of car ownership - the RAC gives the cost per mile for a car up to 1500cc to be 37.3p [3], but only 25% of this is fuel. The other costs are not as energy-intensive as fuel, but manufacture and maintenance clearly involve fossil fuel use.

According to source [2] (Chart D), 26.0 million tonnes CO2 per year (7.10 million tonnes Carbon) arises from fossil fuel use in "Motor vehicle production". This is equivalent to 0.43 tonnes CO2 per person, and this is the estimate used here to derive the factor used.

A second estimate (not used here) is that 0.099 kg/km CO2 arises from UK car maintenance and manufacture, quoted in source [4]. This is equivalent to 0.158 kg/mile, or a total of 38 million tonnes CO2 for the 27 million cars in the UK travelling an average of 9000 miles per year, i.e. a considerably higher estimate.

Construction of roads and their maintenance:
An uncertain amount.

Derivation of the factor used

(Figures are per person per year in the UK where not otherwise specified).

Using the following data:
calculation gives the CO2 emissions from using oil as energy to be 3.67 tonnes per person. Almost all of this is used in internal combustion engines.

Adding the 0.14 tonnes CO2 from oil extraction and the 0.43 tonnes lost in oil refining gives a total energy wasted in oil exploration and refining of 0.57 tonnes, which means that only 3.10 tonnes of the total 3.67 tonnes is actually used in internal combustion engines (an efficiency of 85%).

Allowing for the 0.43 tonnes CO2 arising from fossil fuel used in motor vehicle production, gives a total of 4.10 tonnes per person used in transport, of which only 3.10 tonnes is actually used in internal combustion engines.

CO2 emission rates therefore need to be scaled up by an addition of 32%.

Emissions of 10.9 kg per gallon should therfore be scaled up to 14.3 kg CO2 per gallon of fuel.

Fuel use data have been taken from the Which? magazine Car Guide [7]. These are measured values under real world conditions rather than the manufacturer's published figures under ideal conditions. The published values have been grouped and averaged as follows:
SizeAverage mpggCO2 per mile*
Small, medium, large, city and estate cars52280
MPVs and small & medium SUVs46310
Sports cars and large SUVs35410
*calculated from mpg and CO2 emissions of 14.3 kg per gallon

Miscellaneous points


[1]DEFRA (2007) Guidelines to Defra's GHG conversion factors for company reporting or
[2]Carbon Trust (2006) The carbon emissions generated in all that we consume or
[3]RAC Motoring Services (April 2007) Vehicle Running Costs or
[4]John Barrett, Anthony Scott and Harry Vallack (2001) The Ecological Footprint of Passenger Transport in Merseyside or
[5]BERR Energy Trends December 2007 or
[6]Carbon Trust (2006) Energy and carbon conversions (CTL004)
[7]Which magazine (2019) Car Guide 2019/20
[8]Chris Goodall (2007) How to live a low-carbon life (Earthscan)
[9]AEA Technology (2005) Environmental Costs of Rail Transport or
[10]DEFRA (2007) Act on CO2 Calculator: Public Trial Version Data, Methodology and Assumptions Paper or

First published: 2008
Last updated: 27 May 2021