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CO2 calculator

The climate crisis and what to do about it

Action needed

False and dubious solutions

Awareness raising

Civil disobedience

Reasons for optimism

Tecnicalities by sector

Standards of administration in a democracy

Performance assessments

Best practice examples




Version information

Version 4

The current version of the calculator (Version 4) dates from January 2019 with changes to incorporate the latest emission factors and other information.

The main changes from Version 3 to Version 4 are:

1. Electricity:

The CO2 emission factor was changed to 0.309 kge / kWh from 0.527 kg / kWh.
CO2 emissions have fallen because of the switch from coal to gas in UK electricity generation. (Jan 2019)

2. Typical car fuel use figures

Figures were updated from the DEFRA car emissions factors used in Version 3:
SizeEngine size (litres)mpggCO2 per mile*
small car< 1.5 37 390
medium car1.5 - 2.0 33 430
large car> 2.0 24 600
*calculated from mpg and CO2 emissions of 14.3 kg per gallon


measured values taken from the Which magazine:
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
(Jan 2020)

Version 3

The previous version of the calculator was Version 3, published in March 2008. It is still available at to enable a like-for-like comparison with previous carbon footprint estimates made using version 3.

The main changes in version 3 from version 2 were:
  • electricity: the CO2 emission factor was changed to 0.527 kg / kWh (from 0.43 kg / kWh) to allow for grid losses
  • the reduction for renewable sources of electricity was changed from a 90% reduction to a 25% reduction and restricted to certain tariffs
  • natural gas: the CO2 factor was changed from 0.19 kg / kWh to 0.203 (to allow for supply inefficiencies)
  • CO2 from heating oil was added
  • the factor for cars was changed from 10.5 to 14.3 kg CO2 per gallon (to allow for oil extraction, refinery inefficiency, and motor vehicle manufacture)
  • the basic total for food was increased from 1.4 to 2.2 tonnes CO2 equ. per person, to incorporate information on methane and nitrous oxide emissions in sources [10] and [12].

The factors unchanged were:
  • the CO2 emission factor for bus travel of 100 g / mile
  • the CO2 emission factor for rail travel of 100 g / mile
  • the CO2 emission factor for air travel of 250 kg CO2 equivalent per hour flying

Updates were made in December 2013 to include coal, wood, bottled gas, and newer "green" electricity tariffs.

Cosmetic changes were made in February 2015, together with a change from .htm to .html filetype, but there were no changes to the underlying calculations.

Version 2

This was first published in August 2007 - and was superseded in March 2008.

Version 1

This was first published in February 2007 - and was superseded in August 2007.

First published: 2008
Last updated: 21 Jan 2020