Carbon Methodology

How does the One Small Step Carbon Footprint Calculator work?

Our carbon accounting system is a work in progress. While we’ve put a lot of work and thought into the current model, its accuracy is constrained by:

  1. the information we can collect from you in order to predict your environmental impact; and

  2. the reliance we have presently on self-reporting by users without access to real-world data on things like your energy usage, car usage or kgs of waste you create each week. 


That said, we think the model we’ve built is promising and is only going to get better with time, especially as we look to partner with organisations where we can collate observed data, for example, with your consent, integrating your energy usage numbers through a partnership with your energy provider, or asking questions that help us figure out exactly how often you’re driving your car and it’s fuel efficiency. 


We’ve outlined the methodology we’ve used below to calculate your quiz results in the One Small Step app, and the default assumptions we’ve used to figure out the environmental impact you can achieve by completing the current programs in the One Small Step app. 


We are continuously improving this calculator, and we will update this page with changes to our model as we augment it. 


One big factor that will improve the accuracy of our impact model, specifically for program impact calculations, is the habit-tracking feature we plan to build and release in a few months’ time. This will ask users to log the frequency of things like plant-rich (vegan) meals and cycling trips, so we won’t have to rely as much on in-built assumptions about how often users carry out sustainable behaviours as a result of completing our programs.

Calculating your carbon footprint: methodology and assumptions

We combine the information you provide in your answers to the on-boarding quiz and Australian Bureau of Statistics (ABS) census reports on Australian income, expenditure, water & electricity usage to get a highly detailed breakdown of what your consumer habits are likely to be. These figures are influenced by what state you live in, how many people you live with, and what income bracket your household applies to. 


We then run these energy, water, gas, fuel, food & spending figures through a consumption-based accounting model provided by Tomorrow co. to create an annual CO2e footprint score in each category. This model is used globally and provides localised conversion factors for many countries, including Australia. We then take care to improve accuracy by using recent, Australian-specific data in place of global averages. 


The CO2e footprint data we use is based on ‘full life-cycle analysis’, meaning it takes into account the CO2e produced during material processing, manufacturing, distribution, use, recycling & final disposal of the things you consume. This paints a more complete picture of the effort and  consequences behind consumer goods & services, allowing for more impactful decision-making when trying to reduce our carbon footprint.

Carbon Footprint Quiz Methodology


We use information about your household type, number of residents, occupancy status, income and location to determine which of five electricity usage groups, detailed in the ABS residential electricity usage survey, you would most likely belong to. Your annual usage, (measured in KiloWatt hours, or KWH) is then adjusted to account for any gas water heating, carbon offsetting & sustainable energy sources. Tomorrow co. provides a carbon intensity measurement per KWH for each Australian state (or per MJ – megajoule – if energy source is gas). These have been calculated using real-time consumption statistics and a full lifecycle analysis of each energy production technology provided by the Intergovernmental Panel on Climate Change. We then multiply carbon intensity by your estimated annual KWH usage to get your final energy score. This score is then distributed according to estimates on energy consumption, giving us a look at how much energy can be attributed to appliances, climate, water heating, lighting etc.


Tomorrow co. provides full lifecycle carbon modelling for each transport type per kilometer travelled (e.g. petrol car, hybrid, bicycle, walking etc). Calculations are also distinct for domestic and international flights, as their average air speed, capacities, efficiency & cargo ratios differ. The information you provide allows us to calculate the total distance travelled annually and therefore the total carbon intensity transport score. Options in the onboarding quiz that are a combination of multiple transport methods are calculated using the mean average intensity of those methods. (i.e. Public transport is the average of trains and buses per kilometer travelled).


Referring to your income estimates, we are able to use the ABS household expenditure survey to determine a breakdown of the goods & service expenses you are likely to have. This allows us to estimate the annual carbon intensity of individual products (such as light bulbs), or broader product categories (household durables), depending on the context. These figures are adjusted depending on which state you live in & whether you often purchase second hand. We then map these expenses to a product database provided by Tomorrow co. which estimates the carbon intensity of each Australian dollar spent in those product areas. Some examples of the products and services we are calculating the carbon intensity of are: financial services, clothing, appliances, durables, furnishings, cleaning equipment, electronics, toiletries and so on. We intend to continually add detail to this category as new data becomes available.


We calculate carbon intensity on a per meal basis, using the diet information you have provided. Each diet type has its own adjusted carbon intensity value provided by Tomorrow co., which takes into account age and sex in calculating an average daily intake. The values are further adjusted depending on whether you eat beef and/or dairy and if the food is sustainably sourced. We then calculate the carbon intensity of alcoholic & non alcoholic beverages using the same method as detailed in the purchases category, and add that to get the final score.


We start with the Australian household food & plastic waste averages, add in any disposables from the purchases category (e.g. paper towels, toilet paper etc) and then calculate the carbon intensity using the figures provided by the Tomorrow co. products database. We use adjusted life cycle stats for each waste material type, including average recycling rates. Your final score is then offset by the percentage of your food that is unpackaged & whether you compost your food waste.


The Bureau Of Meteorology estimates the carbon footprint of supplying Australian homes with water in each major district in the urban national report for water utilities. We take the mean of all major districts in each state to get a state average. This does not include the intensity of heating the water, so we have subtracted the total intensity of water heating (gas or electric) from the energy category and added it here for a more accurate look. We then distribute the score using estimates to determine what percentage can be attributed to outdoor use, showers, toilet, laundry etc.

What is CO2e?

Carbon dioxide (CO2) is not the only greenhouse gas that contributes to climate change, but it is one of the easiest to understand, visualise and use in comparisons. CO2 equivalence (CO2e) is the method of converting all other greenhouse gases emitted during production and consumption of goods and services, like methane & nitrous oxide, to their equivalent value in CO2. This gives us a fair look at the relative impact of our actions in simpler terms.

Why do you use a consumption-based accounting model?

We don’t believe you should be responsible for the emissions of all the products your country exports – only for what you consume. We wish to inform and empower you as a consumer, because ultimately the demand of goods and services is in your control. Using a consumption-based accounting model (CBA) also retains accuracy in instances where governments relocate dirty production to nearby countries to maintain a ‘green’ image.

What is the end goal?

It is not too late to mitigate the effects of climate change. Taking into account population growth and natural carbon sinks, the UN estimates that if we reduce our individual yearly footprint to 2 tonnes C02e by 2050, we can limit global warming to 2 celsius by 2100. The ecological and societal outcomes of meeting this target are vast, and our capacity to achieve it improves each year as sustainable energy, transport & food become widespread. If you’d like to find out more, check out the UN Paris Agreement & Global Sustainability Report.

Calculating the estimated impact of One Small Step programs

We have made a series of assumptions about the impact of our existing carbon footprint reduction programs. These are outlined here. All data sources listed are publicly accessible. We think the assumptions we’ve made to calculate program impacts are reasonable and also relatively conservative. 


However we’ll be able to rapidly improve the accuracy of our assumptions with regard to program impacts when we introduce a feature that allows us to track user habits at a more granular level. For now, without that tracking functionality, we have built in default assumptions about user behaviour and how often users carry out a specific pro-environmental behaviour as a result of completing One Small Step programs.

Program impacts scale to fit your existing carbon footprint profile

For different users, programs will have different impacts. This is because One Small Step users have different carbon footprint profiles that affect the potential impact of different programs. Here’s an example of how this works: 


Mike uses the One Small Step app. When he does the quiz, he reports that he is a regular meat eater. When Mike completes the ‘Discover Plant-based Food’ challenges and starts switching to vegan alternatives, we assume he commits to eating two vegan meals per month for 2 months. By calculating the difference in intensity of those vegan meals as compared to his current diet we are able to estimate his impact.


When Chrissy does the quiz, she reports that she is a vegetarian. By using her current diet in the calculation, we get a lower, but more accurate, potential impact for Chrissy than for Mike.


This convention is used wherever possible to help keep the total impact of completing programs consistent with who you are, and the sustainable habits you already have committed to prior to coming into the app.

Program Impact Assumptions

Discover Plant-Based Food

We have set a default assumption that if the user completes this program, they eat an additional 16 vegan meals in total. That equates to roughly two vegan meals per week for 8 weeks (from a total of 168 meals over 8 weeks). These 16 meals cause 15.4kg CO2e. So the impact from this program comes from taking the user’s existing CO2e footprint for 16 meals based on their current diet (as reported in the quiz) and then subtracting the emissions caused by the 16 vegan meals to arrive at the assumed program impact figure.

If the user is already vegetarian or pescatarian, then their total CO2e impact is lower from this program, because the emissions associated with their existing meals were lower than for a user who regularly eats meat and dairy.
Caveat: We may have under-estimated or overestimated emissions impact from this program, depending on how much more plant-rich food the user starts eating during and after the program. We’ll be introducing a feature that allows users to track their plant rich meals through a habit tracker, which will remove the need to estimate meals and allow the user to report this figure themselves. This will significantly improve the accuracy of this program’s calculated impact.

Food, Not Waste Program

This program, once completed, assumes that of the compostable food you were previously putting in the bin, you are now composting 80% of it. Someone who reported as ‘sometimes’ composting their food waste in the on-boarding quiz will have a lower program impact because they were already composting about 50% of their compostable food waste. Compostable food = food that can be composted. So for wasted food that isn’t typically compostable - e.g most meat and dairy - this is not included in the assumed impact (we assume this is still going in the bin).

On Yer Bike Program

We have assumed for this program that the user, after completing the program, starts riding one day a week. We calculate the impact of this weekly ride based on the user’s reported commuting distance and their usual mode of transportation (as reported in the on-boarding quiz). So if the user ordinarily commutes 5-10km each day in their car, we take the assumed carbon footprint from that single car trip and remove it - since now the user is using their bike to make that trip instead of driving, just once a week. If the user is usually catching public transport, the impact of this program footprint will be lower, but only because they already had lower transport-related emissions due to their use of public transport instead of using a single-passenger vehicle. If the user reports that they ordinarily walk as their main mode of transportation, then the impact from this program is slightly negative (since you generate zero emissions from walking and a tiny amount of emissions from cycling due to the embodied emissions in the purchase of the bicycle).

Caveat: We may have under-estimated or overestimated emissions impact from this program, depending on how much more frequently the user starts cycling during and after the program. We’ll be introducing a feature that allows users to track the frequency of their cycling and walking trips through a habit tracker, which will remove the need to estimate rides for the year, and allow the user to report this figure themselves. This will significantly improve the accuracy of this program’s calculated impact.

Energy Saving at Home Program

For the ‘Big Switch Off’ challenge, we assume the user eliminates 3% of their energy usage for the year. This assumes they continue with the practice of switching most appliances off at the power point when not in use and switching off lights when not in use. This 3% reduction in total home energy consumption is taken from the Australian Federal Government’s AusHome.Gov figures. For the ‘Let There be LED Light’ challenge, we assume that if you have completed this challenge then the carbon footprint associated with your lighting (based on the energy that your lights consume) is reduced by 80% as a result of switching to LEDs. This 80% reduction in energy consumption for LED lights compared to standard lights is based on figures from the Australian Federal Government’s Aushome.Gov site. For the ‘Natural Heating Hacks’ challenge, we have assumed that the energy usage associated with climate control of your home (that is, the energy that goes into heating and cooling your home) has been reduced by 10% through better insulation of windows (ours is a conservative assumption). We have taken this percentage change in climate control-related energy usage reductions due to better window insulation from the Aushome.Gov website. For the ‘Draughts: Seek and Destroy’ challenge, we have assumed that the energy usage associated with climate control of your home (that is, the energy that goes into heating and cooling your home) has been reduced by 7.5% through better insulation of windows and doors through draft proofing (this is a conservative assumption). We have taken this percentage change in climate control-related energy usage due to better insulation through draught proofing from the Aushome.Gov website. For the ‘Switch to carbon neutral’ challenge’ we have assumed a 82% reduction in the emissions associated with the user’s home energy usage. For the Invest in GreenPower challenge, we have not assigned any impact to the user switching to GreenPower since this step is 1) optional and 2) we do not know the percentage of GreenPower the user is now buying month-to-month to effectively offset their electricity-related emissions.

Green Finance Program

We assume that by marking the challenges in this program as completed, that you have switched your banking over to a fossil fuel-free bank and you have switched your superannuation over to a fossil fuel free superannuation fund. By surveying you about your average income in the on-boarding quiz, and using ABS data on income quintiles, we generate an estimate for your assumed financial savings (based on the typical amount of money saved for someone with your household income), and apply a carbon emission factor (based on Tomorrow Co. emissions intensity figures for financial services and localised data) to this dollar amount to create the initial carbon footprint for your money in the bank. At present, we assume that if you switch to a green bank, your money has 80% less emissions intensity associated with it than in a regular bank. For banks such as Beyond Bank, this would in reality involve a 100% reduction in emissions associated with your bank account money, because it is a fully carbon neutral bank. CAVEAT: Benchmarking emissions associated with financial services, specifically, the average emissions intensity of your savings account dollars and super balance, is difficult. It is also hard to estimate the difference in embodied emissions on average when you switch to a green bank or super fund. We are working hard to improve the accuracy of our assumptions here through additional research over the next few months.

Sustainability at Home Program

A lot of the challenges in the Sustainability at Home program teach foundational skills to support a more sustainable lifestyle, particularly with regard to habits that significantly reduce food waste. We’ve assumed for the food-related challenges, that users will continue the behaviours they learn in each challenge for the remainder of the year, cooking stock from time to time, picking some veggies occasionally and sometimes making jams. We have assumed a 15% reduction in food waste if the user learns how to make stock and continues to do so through the ‘Stock up’ challenge, which equips the user to make stock from vegetable scraps and meat scraps that would otherwise go in the bin, and with the ‘Pickled Tink’ challenge to pickle vegetables rather than throwing them in the bin, we assume a 5% reduction in total food waste. We have assumed that from the ‘We’re Jammin’’ challenge to make your own jam, and the ‘Growing from scrap’ challenge to grow vegetables from food scraps, that users achieve an overall reduction in the carbon intensity of their meals of 1% for each of these challenges that are completed. Similarly, we assume you continue to use your beeswax wraps and no longer purchase clingwrap, which leads to a 10% reduction in plastic waste (and therefore a 10% reduction in the emissions associated with your plastic waste), and that from the mending activities performed in the Clothes Mending challenge (we assume mending roughly 3-4 T-shirts or sweaters on average), you avoid replacing those items and extend their lifetime.

  • Facebook
  • Instagram
  • Twitter
  • LinkedIn

Supported by City of Melbourne through the Social Enterprise Grants program

© 2020 by The Neighbourhood Effect Pty Ltd. All rights reserved.