How to Choose a Carbon Calculator

Companies are under a fair amount of pressure to understand what their impacts are across their value chains. The image above is from the Greenhouse Gas protocol and gives a great visual overview and break-down as to the different emission categories that a company can report on. Companies normally go through a scoping exercise to work out all of their activities to start collecting the raw data and then apply specific emission factors from providers such as the Department for Environment, Food and Rural Affairs (DEFRA) in the UK or the Internal Energy Agency (IEA).

Often as individuals we ask ourselves, what can we do to try and reduce our impact on this planet? What if we were to apply the same framework as companies to our own lives and see where the material hotspots are?

The first step of applying this framework is quantifying our individual carbon footprint. Without the resources available to companies, that leads us to various free carbon calculators available on the web.

To quantify our footprint, we need to understand where our impact is coming from. Emissions will fall into a few main categories called scope 1, 2 and 3 emissions. At a very high level, below is a simple screening of the areas you will need to assess for your overall emissions profile.

Scope 1: Direct emissions from owned or controlled sources

  • Petrol (gasoline) or diesel for your vehicle
  • Fuel oil, coal, LPG, Propane, wood for your heating
  • Natural gas or LPG for cooking or heating
  • Refrigerant gases from air conditioning units

Scope 2: Indirect emissions from the generation of purchased energy

  • Purchased electricity, steam, heating or cooling for your home use

Scope 3: Indirect emissions from upstream or downstream

Purchased goods and services

  • Groceries (meat, pescatarian, vegetarian, vegan)
  • Clothing and shoes
  • Computers/phones/headphones/tablets and any other IT equipment
  • Hotel/motel nights
  • Restaurants and eating out
  • Vehicles
  • Furniture for your house
  • Insurance
  • Online services (music/anti-virus/data or cloud storage/emails/internet/phone)
  • Other services including water charges, rates/council tax

Fuel and Energy related activities

  • These are the indirect emissions related to Transmission and Distribution (T&D) of electricity or the process of Well To Tank (WTT) resulting from the production, transportation and distribution of fuels.


  • Domestic, medium, long haul air travel and the different classes (economy, premium economy, business, first)
  • Taxi, bus, long distance bus, train, tram, tube/subway, boat/ferry

Waste generated at home

  • Reuse/donation, recycling, composting, landfill, waste to energy


  • Kiwisaver & pensions / retirement savings, shares, bank savings

What I have often found is that free carbon calculators do not show the full picture for an individual’s emissions due to the variability in categories they offer for the end user. That being said, it is a good start to see what your emissions are.  So, what should you be looking out for when using one of these calculators to give the best representation of your individual emissions?

Let us take an example of an individual and plug this consumption data into a few online calculators to see what we get. This data is based on a couple living in a two-bedroom apartment, a low meat consumption diet in the United Kingdom, and air travel for one single person.

Table summarising the assumptions made to calculate an individual footprint, as well as the total calculated carbon emissions based on each calculator

Calculator 1:

This first calculator only lists household energy (Scopes 1 & 2), business travel, waste and had no other scope 3 categories. Household total emissions came out at 13,300 kgCO2e per year. This was a New Zealand specific calculator so you couldn’t adjust your home or waste emissions to any other country, and I could not choose the travel class for the air travel component so assume they have used a generic class factor and included radiative forcing.

Note: Emissions coming from planes at a higher altitude have a much greater impact on climate change compared to emissions released at ground level. Particulate matter from fuel combustion (soot) causes contrails and this causes Radiative Forcing (RF) (Bock & Burkhardt, 2019). Organisations such as DEFRA publish two factors for air travel, one with radiative forcing and one without, but the recommendation is now to use the ‘with RF’ factors (DEFRA, 2019).

Calculator 2:

Calculator two had the household total at 15,200 kgCO2e with an overview of what they term as secondary emissions based on spend. I liked the breakdown of secondary spend the most with this calculator, however, you would need to have a good understanding of your monthly or annual spend on food, clothing, hotel and holidays, insurances, home furnishings etc. These factors are sourced from DEFRA and have been corrected to account for inflation. This calculator also allowed the user to select between travel classes and adding radiative forcing or excluding it. For the purposes of comparison, I have included both in the table and included radiative forcing in the emission totals.

Calculator 3:

The WWF calculator had a series of questions it would ask you to consider when completing the carbon footprint. This one had the second highest total being 20,300 kgCO2e with travel contributing the highest amount and it is again assumed travel is a generic class with radiative forcing.

Calculator 4:

Finally, using the same consumption data, the fourth calculator gave a total of 24,170 kgCO2e household emissions.

There were more categories in this calculator to cover scope 3 impacts. However, air travel seemed to convert the locations of airports into flight time, instead of distance (where distance is more accurate). This therefore meant there was a noticeable difference in the air travel data even though the trips entered were exactly the same.

The best calculator that I found for personal emissions was calculator two. This is because it allowed the user to select the country and the associated emission factors. It is important to ensure you select the country you are living in because the most accurate country emission factors are then behind the calculations.  The second calculator had the best overview when it came to an individual’s indirect emissions, even if the data being entered is financial. It also allowed users to select between classes when entering air travel.

Ready to give the calculation a try? Here are some tips on what to look out for:

  • Try to find a calculator local to your country, or one that will at least enable you to select your location. This is important as electricity grid mixes will differ for each country, for example the grid mix of New Zealand will have a lower impact due to the wind, hydro and geothermal components compared to the grid mix from China or Australia. This means your electricity or public transport (electric trains/ busses) emissions will vary depending on these country differences.
  • Check if the calculator adjusts for the class of travel and the inclusion of radiative forcing when it comes to air travel, i.e. selecting between business and economy and if it includes radiative forcing. This will have a significant impact on the emissions from your air travel as an individual.
  • Find a calculator that will cover a range of scope 3 categories and not just business travel and waste. As you can see in our example, the inclusion of purchased goods and services is important as these are material emissions in your overall individual profile.

Now that you have more accurately assessed your impacts, the next piece in the puzzle is to start coming up with targets and an action plan to try and reduce your impact.

Josef de Jong is the owner and principal consultant at Perdure Carbon. His passion for sustainability started during his undergraduate degree at the University of Waikato in New Zealand before going on to gain a Masters in Management and Sustainability. His international career has seen him working in Germany, New Zealand and the United Kingdom over the past nine years as a sustainability consultant for corporate clients. 

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