What Is a Carbon Footprint (and How Do You Measure It)?

A carbon footprint is the total amount of greenhouse gases produced by a person, product, company or activity, expressed as tonnes of CO₂ equivalent (tCO₂e). It bundles several different gases into one comparable number, which is what makes it a useful — if imperfect — way to size up your climate impact.

What "carbon footprint" actually means

• More than just CO₂. The term covers all major greenhouse gases, not only carbon dioxide from burning fuel.
• Measured in CO₂e. Methane, nitrous oxide and others are converted into a single "carbon dioxide equivalent" figure so different gases can be added together.
• Why the conversion matters. Methane traps far more heat than CO₂ over 100 years, so 1 tonne of methane counts as roughly 28–30 tonnes of CO₂e.
• It scales to anything. You can calculate a footprint for a single flight, a T-shirt, a household or an entire multinational.
• A typical benchmark. The average person in the UK is responsible for around 7–10 tCO₂e per year; the global average is closer to 4.7 tCO₂e.

Direct vs indirect emissions: the three Scopes

To keep footprints consistent, emissions are usually split into three "Scopes". Scope 1 is direct emissions from sources you own or control, such as a company car or a gas boiler. Scope 2 is indirect emissions from the electricity, heat or steam you buy. Scope 3 is everything else in your value chain — suppliers, business travel, product use and disposal — and for most organisations it is by far the largest and hardest slice to measure. A personal footprint follows the same logic: the fuel you burn directly, the energy you buy, and the emissions embedded in the food, goods and services you consume. If you want to translate a specific activity into tonnes, the free Evertreen CO₂ calculator is a quick starting point.

How a carbon footprint is measured

At its core, measuring is simple arithmetic: activity data × emission factor = emissions. Activity data is how much of something you did — litres of fuel, kilowatt-hours of electricity, kilometres driven, kilograms of beef. An emission factor is a published figure for how much CO₂e each unit produces, drawn from national databases and standards like the GHG Protocol. Multiply the two, repeat across every source, and add them up. Consumer calculators do this behind the scenes using averages, so they give a reliable estimate rather than an audited number. The same transparency principle guides how Evertreen works out the climate impact of planting — you can read our full method for how we estimate tree CO₂ rather than relying on a single headline figure.

Where the numbers come from — and why they disagree

Two credible sources can give you different answers for the same activity, and it is almost always one of these four reasons:

• Boundary. Does a flight's figure include only fuel burnt, or also non-CO₂ effects at altitude and the fuel supply chain? Both are defensible; they are not the same number.
• Production vs consumption. National figures usually count emissions produced inside the borders. Consumption-based figures add imports and subtract exports, and are typically higher for wealthy countries.
• Vintage of the factor. Grid electricity factors change every year as the generation mix changes. A 2019 factor applied to 2026 electricity overstates the result in most European markets.
• Allocation choices. How you split the footprint of a shared lorry, a shared building or a multi-product factory is a methodological decision, not a physical fact.

None of this makes footprints useless. It makes them comparable only when the method is stated — which is why any serious footprint disclosure publishes its boundary and factor sources alongside the number.

Footprints of things people actually ask about

Rough orders of magnitude are more useful than false precision. Broadly speaking:

• A long-haul return flight lands in the low single-digit tonnes per passenger — comparable to an entire year of a modest lifestyle in many countries.
• A year of home heating with gas is typically the largest single household line in a cold climate.
• A kilo of beef carries an order of magnitude more emissions than a kilo of most plant proteins.
• A smartphone spends most of its footprint on manufacturing, not charging — which is why keeping it a year longer beats optimising how you charge it.

The pattern is consistent: manufacturing and fuel dominate, and behavioural fine-tuning at the margins rarely changes the ranking.

Why measuring comes before acting

You cannot reduce what you have not measured. A footprint reveals where your emissions actually sit — often somewhere surprising, like your supply chain or your diet rather than your car — so you can cut the biggest sources first. The credible sequence is measure, then reduce, then offset only what genuinely remains. For those residual emissions, Evertreen lets you fund reforestation from just £1.5 per tree, with every tree geolocated by GPS pin, tracked with progress photos and backed by on-the-ground field videos from our planting teams. Certified Verra and Gold Standard carbon credits are available on request for organisations that need formal claims. You can start with a single tree or a full Evertreen tree-planting project and follow exactly where your contribution goes.

Next steps depend on who you are: individuals should start with how to calculate your personal carbon footprint; businesses with how to calculate your business carbon footprint. Either way, reducing comes before compensating.

Frequently asked questions

What is the difference between CO2 and CO2e? CO₂ refers to carbon dioxide alone, while CO₂e (carbon dioxide equivalent) rolls all greenhouse gases — including methane and nitrous oxide — into one comparable number based on their warming power.

How can I measure my own carbon footprint? Multiply your activity data (energy use, travel, diet) by published emission factors, or use a free tool like the Evertreen CO₂ calculator to get a solid estimate in a few minutes.

Does planting trees reduce my carbon footprint? Trees absorb CO₂ as they grow and can offset residual emissions, but they work best after you have measured and cut what you can — offsetting complements reduction rather than replacing it.

What is a carbon footprint measured in? Tonnes of carbon dioxide equivalent (tCO₂e), which converts every greenhouse gas into the amount of CO₂ that would cause the same warming.

Who invented the idea of a carbon footprint? The concept grew out of ecological footprint research in the 1990s and was popularised in the 2000s, including by fossil-fuel marketing that emphasised individual responsibility. The tool is still useful; the framing deserves scepticism.

What is a product carbon footprint? The emissions from one item across a defined life cycle — raw materials, manufacture, transport, use and disposal — which is why two products with the same weight can have wildly different footprints.

Is a smaller footprint always better? As a direction of travel, yes, but the number alone can mislead: a footprint that shrinks because you outsourced production has moved the emissions rather than removed them.