How to calculate your carbon footprint

By Ruari McCallion

October 2023

Why and how to use online carbon footprint tools

‘If you don’t measure it, you can’t manage it’. Ruari McCallion looks at carbon footprint calculators and assesses their general value.

How important is it that businesses know what their carbon footprints are? Customers, especially other businesses, want to know what they’re buying, for example, and how responsible their supplies are. Looking forward, legislation requiring businesses to know and to publicise their carbon footprint is likely.

Calculating the carbon footprint of a small business involves estimating the greenhouse gas emissions that are generated both by various activities within the organisation and by its business supplies – a factor often forgotten or overlooked. Items like stationery, computers, tablets and even office furniture also have a carbon footprint.

Items like stationery, computers, tablets and even office furniture also have a carbon footprint

Knowledge is power

Knowing can help to improve management of energy, emissions and efficiency, especially of vehicle fleets. Within a building, better management of power supplies can have a significant impact on bills, cost base and, ultimately, profitability.

Carbon footprint calculators can be helpful in estimating and raising awareness about individual emissions across the organisation. Their ultimate accuracy and effectiveness will depend on various factors.

They all rely on information provided by the user, so it’s important that data about energy consumption, transportation habits, operational environment and energy-saving practices are accurate.

Different calculators may focus on different aspects. Some calculators provide quite a detailed analysis while others may offer a more general picture with, perhaps, the opportunity to drill down further.

While energy sources will be differentiated – say, between electricity and natural gas or LNG for heating – the source of electricity may not always be identified. In France, for example, most electricity is generated by nuclear power stations and is zero carbon, while Germany has an increasing proportion of coal-fired energy generation. The mix in other countries can be anything but straightforward.

There is no universal standard; different calculators may use different methodology, leading to different results from the same inputs.

Bearing these limitations in mind, they are useful tools.

Define your parameters

When preparing to make your calculation you should consider whether you want to include only direct emissions from activities under your direct control or to include indirect emissions from the value chain. Whatever you decide, direct comparisons can only be made by comparing like with like.

Calculators are quite easy to find online. In the UK, the Carbon Trust offers a free calculator that is designed specifically for small and medium-sized enterprises (SMEs) (SME Carbon Footprint Calculator | The Carbon Trust). It covers a range of emission sources, including energy, transport, waste and water. In the USA, the Environmental Protection Agency (EPA) offers a simple and user-friendly calculator for SMEs (Carbon Footprint Calculators for Businesses – Carbonfund).

The SME Climate Hub (Start measuring – SME Climate Hub) uses a calculator provided by Swedish company Normative and is available across much of the world. It is sponsored and supported by partners of the UN’s Race to Zero campaign. ecocockpit (ecocockpit – CO2 balancing for companies), is geared towards Germany. If you Google ‘carbon footprint calculator’ you should find others in your own language and country.

Ease of use

Carbon Trust and Normative were both pretty easy to use. I entered details of Lockeran/Eureka, an imaginary small business, operating a warehouse extending to 1,000 square metres, with five employees and revenues of £500,000 or €500,000. Electricity consumption was entered as 29,000 kWh a year; natural gas at 1,000 cubic metres. It has three petrol-driven vehicles consuming 1,500 litres annually. Total diesel consumption, based on two forklifts, three vans and a generator, is 10,000 litres. The Euro-denominated business was stated to be located in France.

Normative wanted quite a lot of detail, which will probably turn out to be useful for businesses operating in the real world.


Total annual CO2 emissions were calculated by Normative to be 67.7 tonnes. Just about half (32.5 tonnes) was from fuel combustion – petrol and diesel – which is described as ‘Scope 1: direct emissions from sources owned or controlled by the business’. Under ‘Scope 2: indirect emissions from purchased electricity, heat or steam’, emissions were very low, at just 1.41 tonnes – but bear in mind France’s nuclear-generated electricity. ‘Scope 3’ covers ‘business travel, capital goods and purchased goods and services’. Capital goods, including machinery, office furniture and computers, amounted to a somewhat alarming 24.8 tonnes

carbon results

The Carbon Trust results came in three sections. It provided a very clear pie chart that showed HVAC (41%) to be the lead consumer of energy but only just ahead of lighting, at 40%. I told it that we did not have automatic dimmer or switch-off systems in the facility. It said that current usage was within industry norms but also identified a ‘quick win’. My fictitious company could save £1,879 a year by upgrading its lighting system and controls, for an initial investment of £2,256 to £3,739, giving ROI (return on investment) in two years or less. The kWh savings amounted to a little over one sixth of the total, at 5,526 a year.

Interestingly, the Carbon Trust reported a much lower total than Normative, at 34.35 tonnes. This was largely explained by the absence of Scope 3 emissions in the initial calculation. The offer was there to go back and drill down further. Scope 1 emissions amounted to 82% of the total and Scope 2 to 18% – much higher than Normative and reflecting, again, assumptions of French nuclear-generated electricity.

It was an interesting and illuminating exercise, although the results from these two were quite different; businesses must make sure they are inputting the correct data and assumptions, or the results could be very misleading.

Calculating a carbon footprint is an iterative process – there is always room for improvement and regular revisitation will help to identify opportunities and measure progress.

Dimmer switches and improved insulation are on order!