How do we calculate our greenhouse gas emissions?


If you are like many other organisations, you will be keen to understand how you can reduce your greenhouse emissions… but where do you start and where do you concentrate your efforts? 

To know where to make reductions you must first identify and then establish the significance of each source of greenhouse gas emission in your business and supply chain. Although some sources of emissions are easy to calculate accurately, others are more complex. Don’t let this intimidate you… we have outlined below the starting point for how to calculate your emissions groups.

For more information on what Scope 1, 2 and 3 are, please see our previous article:


Scope 1 Emissions


  • If you use gas to heat your water or for heating, get hold of your gas bills – first you will need to identify how much you have used in kWh (on a monthly or annual basis) and then you will need to determine the emissions per kWh. The bills often tell you the emissions related to each kWh, or will at least point you to an online source which gives this information. If you cannot find the emissions related to your exact gas usage you can do a simple calculation to convert the gas measurement into kgCO2e emissions using the conversion factor in the government produced data set.

Fuel in plant and company cars

  • If you purchase fuel for company owned (or leased) vehicles or plant, collect information related to the purchase of fuel. You will need to convert either the volume of fuel used; the mileage driven; or the amount spent (depending on your data) into kgCO2e emissions. Data on the conversion factors can be found in the government produced data set.
  • If you have electric vehicles charged using company electricity, this will be captured in Scope 2.
  • Air conditioning – If you have significant use of air conditioning check your servicing records and establish if any of the gas has leaked. If there is a release you will need to determine the type and quantity of the refrigerant and the related CO2e emissions.


Scope 2 Emissions


  • These emissions are related to the amount of electricity you use on site. Collect your electricity bills to determine how much electricity you are using in kWh. You will also need to determine the energy mix, i.e. how is your electricity made, coal? nuclear? renewables? a mix if the above?
  • On some bills the energy company will tell you the exact mix and the related CO2e emissions per kWh. If you are not that lucky you will need to find out the mix from the energy company or in the worst-case scenario base your calculations on grid averages which can be found here in the government produced data set.


Scope 3 Emissions

This is where you will need to do some exploration and apply judgement as to which emissions you want to monitor. Of the 15 categories of scope 3 emissions only some will be significant depending on the type of business you are in. The way in which you calculate the emissions will vary depending on how much data you have. The reality is that you won't have a complete set of data so you will need to make assumptions and justifications to determine the emissions.

This can take some experience, and you have a couple of options. You can either read up and study how to calculate these scope 3 emissions (there are some good resources about – we recommend starting with the GHG Protocol Scope 3 guidance), or you can engage a third party to undertake these calculations for you.

You do not need to address every scope 3 emission; however, you should try and address all those which are material. Some typical methods to gather data are as follows:

  • Travel for work – This would include collecting data on flights, trains, taxis, tube but only where each of these are not for commuting (e.g. getting to the main place of work). Distance data should be collected on all travel for work, and converted to kgCO2e using the government produced data set. Where spend is known but distance is not, this will need to be converted to distance and then have the conversion applied.
  • Employee Commute – This is for travel from home to the office. Generally this data can be collected by issuing a survey that asks employees to complete information on their typical commute. I.e record the mileage they travel, the transportation method and frequency. You can calculate emissions by multiplying the distances by the emission factors in the government produced data set.
  • Remote working – Although there is no official data on the average figures for electricity and gas usage at home a widely used source is the Ecoact whitepaper. If you want to produce a more accurate figure, you may want to ask employees if they use renewable providers of electricity, otherwise you could apply the average grid electricity emission factors found in the government produced data set.
  • Purchased services – These are GHG emissions from third party services – consultants, cloud computing, accountants etc. Typically you can export your spend on services from your accountancy software and use the ONS data set to approximate emissions for each service sector based on spend.
  • Purchased goods – Depending on your industry this could be a significant source of your emissions. This category can be highly involved but for an office based service business you will want to look at emissions related to purchases such as computer equipment – a lot of electronic equipment has good data attached to it, for example see this Macbook data sheet. Try a search with the device model followed by ‘environmental data sheet’. If you are a manufacturing or construction company you will need to either get data from suppliers, or refer to sources such as the government produced data set which has details of emissions related to certain materials.
  • Waste – Depending on your industry, waste may represent a large or small part of your emissions. Once you have collected data about the amount of waste you produce (e.g. from waste transfer notes) and the method of end of life treatment (recycled, landfill, energy for waste etc.) you can use the government produced data set to convert this to emissions.
  • Upstream transportation and distribution – This includes transportation and distribution of products between your supplier and yourself (in vehicles not owned or operated by you); and third-party transportation and distribution services purchased by you including inbound logistics, outbound logistics (e.g., of sold products), and third-party transportation and distribution between your own facilities. It is really important to note that emissions relating to sold product for which you pay the distribution counts in the upstream category. You will need to look at all shipments and the associated distances (including vehicle type/transport method). Then use the government produced data set to arrive at emissions.
  • Downstream transportation and distribution – Where a customer pays for the transportation or distribution, the emissions should be recoded in this category. You will need to look at all shipments and the associated distances (including vehicle type/transport method). Then use the government produced data set to arrive at emissions.
  • Transmission and distribution – This category is associated with the losses that come from distributing power to your office/employee houses. Total all your electricity usage in kWh and then apply the conversion factor in the government produced data set for distribution losses.

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