Carbon footprint: what it is and how to calculate it step by step

To measure your company's carbon footprint today you need four things: define the organisational boundaries and the year you will analyse, collect activity data (kWh, litres, kilometres, kilograms), multiply each figure by its official emission factor and add the results up in tonnes of CO₂ equivalent. The formula never changes: activity data times emission factor.

A carbon footprint is the total amount of greenhouse gases (GHG) released into the atmosphere, directly or indirectly, by a person, organisation, product or event over a defined period, usually one year. It is expressed in tonnes of CO₂ equivalent (CO₂e), a unit that brings different gases together into a single comparable figure.

What exactly is a carbon footprint?

The carbon footprint quantifies the impact an activity has on the climate through the GHG emissions it causes. It is not limited to carbon dioxide: it accounts for every greenhouse gas, weighted by its capacity to warm the atmosphere, and translates them into a single figure in CO₂ equivalent.

Measuring is the first step to reducing. Without a baseline calculated using a recognised method you cannot set a target, prioritise investment, answer a customer asking for emissions data, or bid for a public contract with environmental criteria.

Which gases are included and how are they converted into CO₂ equivalent?

The Kyoto Protocol recognises seven greenhouse gases, and any of them can form part of a footprint:

• Carbon dioxide (CO₂): the most abundant, linked to burning fossil fuels.
• Methane (CH₄): livestock, landfills and waste management.
• Nitrous oxide (N₂O): fertilisers and agricultural and industrial processes.
• Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs): refrigeration and industrial processes.
• Sulphur hexafluoride (SF₆) and nitrogen trifluoride (NF₃): electrical equipment and electronics.

Each gas is converted into CO₂e by applying its 100-year global warming potential (GWP). Using the values from the IPCC Sixth Assessment Report (AR6), which are the ones published in the GHG Protocol reference table, fossil methane has a GWP of 29.8 and nitrous oxide 273. One kilogram of N₂O is therefore equivalent to 273 kilograms of CO₂.

What types of carbon footprint are there?

Four approaches, depending on what is being measured:

• Personal footprint: emissions from a person's everyday activities, such as home energy use, mobility, food and waste.
• Product carbon footprint (PCF): the impact of a product across its entire life cycle, from raw material extraction to end of life. It is governed by ISO 14067:2018.
• Event footprint: the impact of conferences, festivals or competitions. In Spain, external verification is mandatory to register the footprint of large events in the MITECO registry.
• Corporate or organisational footprint: the emissions of a company's entire activity, organised into the three GHG Protocol scopes. This is the one customers, banks and public tenders ask for.

Which scopes does a company have to include?

Royal Decree 214/2025 requires companies to calculate their Scope 1 and 2 footprint, publish it free of charge on their corporate website and draw up a reduction plan with a quantified target over a minimum five-year horizon. It applies to companies that already prepare the non-financial information statement: more than 250 employees plus either public-interest entity status or exceeding, over two consecutive financial years, 20 million euros in assets or 40 million euros in turnover. Registration in the MITECO registry remains voluntary for private companies; it is only mandatory for the state public sector, from 2026, with Scope 3 from the 2028 calculation onwards.

Scope 3 usually represents the largest share of the corporate footprint and is also the hardest to measure, because it depends on supplier data. You can go deeper into the difference between scope 1, 2 and 3 emissions and the 15 categories of scope 3.

How do you calculate a company's carbon footprint, step by step?

1. Set the period and the boundaries. Choose the year to analyse (RD 214/2025 allows any twelve consecutive months, not necessarily the calendar year) and decide which legal entities, sites and facilities are in, using operational control or equity share.
2. Choose the standard. ISO 14064-1:2018 is certifiable and is the reference if you need a verified report. The GHG Protocol Corporate Standard is the most widely used methodological framework and organises emissions into three scopes. They are compatible: see the detail in our comparison of GHG Protocol and ISO 14064-1.
3. Inventory your emission sources. Go facility by facility: boilers, furnaces, generators, vehicles, air-conditioning equipment with fluorinated gases, and contracts for electricity, gas, water and waste.
4. Collect activity data. Actual consumption from invoices and meters, litres refuelled, kilometres driven, kilograms of waste per operator, purchases. Favour measured data over estimates and keep the source document.
5. Assign an emission factor to each data point. One factor per fuel type, country and year. Always record the source and version of the factor you used.
6. Calculate and consolidate in CO₂e. Multiply, apply each gas's GWP and add up. Present the result by scope and by site.
7. Analyse and verify. Identify hotspots, compare against the previous year and, if you need an auditable report, commission verification of your carbon footprint by an accredited body.
8. Define the reduction plan and repeat every year. Without a time series there is no demonstrable progress. Here is how to structure a carbon footprint reduction plan.

What is the carbon footprint formula?

The formula published by MITECO in its official calculation guide (May 2026 version) is:

Carbon footprint = activity data × emission factor

Activity data is the measured consumption: litres of diesel, kWh of electricity, kilometres driven, kilograms of waste. The emission factor tells you how many kilograms of CO₂e each unit of that consumption generates.

Worked example using official MITECO factors for the 2025 financial year, in a company with a heating-oil boiler, two petrol cars and 20,000 kWh of electricity:

The result is 53.05 tonnes of CO₂ equivalent. The same operation is repeated for every source and added up. The real difficulty is not the multiplication: it is getting complete activity data and picking the right factor for each line.

Where do official emission factors come from?

To register a footprint in the Spanish registry the rule is explicit: Scope 1 and 2 factors must be the ones MITECO provides through the registry website, and the electricity mix factor must be the one published by the National Markets and Competition Commission (CNMC) for each supplier. This is set out in the registry support document, version 19, April 2026.

Three practical rules: use the source of the country where the consumption happens, store the factor's version and year alongside the data, and never mix factors from different years within the same inventory. For a wider view of the frameworks involved, see our overview of the main carbon footprint measurement standards.

What tools are used today?

A single-site company can start with the MITECO spreadsheet. As soon as there are several facilities, a fleet, suppliers and more than one country, the spreadsheet stops holding up: traceability is lost, factor versions get mixed, and every annual close turns into a project.

The Manglai platform, with clients in 70 countries, more than 30,000 users and 25 million tonnes of CO₂e managed, automates the full cycle:

• Automatic data collection through invoice reading for energy, water and fuel, plus integration with ERP and fleet systems.
• Calculation across all three scopes with up-to-date official factors and traceability of every figure back to its source document.
• Dashboards and auditable reports by site, by scope and by category.
• Reduction scenario modelling and plan tracking.
• Reporting preparation for the CSRD or for the MITECO carbon footprint registry and its Calculo, Reduzco and Compenso seals.

Frequently asked questions about calculating a carbon footprint

In what unit is a carbon footprint measured?

In tonnes or kilograms of CO₂ equivalent (CO₂e), a unit that groups all greenhouse gases weighted by their 100-year global warming potential.

Can I calculate a carbon footprint in Excel?

Yes, and for a small organisation with few sources it is perfectly reasonable. The problem appears with multiple sites, a fleet and suppliers: at that point the risk is not the arithmetic but data traceability and factor version control, which is exactly what a verifier reviews.

Is my company required to calculate its carbon footprint?

If it has more than 250 employees and is either a public-interest entity or exceeds 20 million euros in assets or 40 million in turnover over two financial years, yes: RD 214/2025 requires calculating Scopes 1 and 2, publishing them and having a reduction plan. Many SMEs calculate it anyway because customers or public tenders ask for it.

Is external verification required?

To comply with RD 214/2025 without registering, no. To enrol in section a) of the MITECO registry, third-party verification is required, except for the cases listed in article 6.6 of the royal decree: SMEs, associations, foundations, cooperatives and public administrations whose significant emissions all have published factors.

What is the difference between a carbon footprint and climate neutrality?

The footprint measures emissions. Climate neutrality is reached when those emissions are cut as far as possible and the remainder is offset, so that the net balance is zero.

How often should it be recalculated?

Once a year. Comparing financial years is what allows you to demonstrate reductions, and the MITECO Reduzco seal requires four consecutive years of data to compare two overlapping three-year periods.

The first step is always to measure. You can run an initial estimate in a few minutes with Manglai's free carbon footprint calculator, or see how we automate calculation and reporting across all three scopes in the carbon footprint solution.