What this estimator does — and what it does not
This estimator adds three figures — home energy, travel and everything else — into an annual total in kilograms of carbon dioxide.
It does not derive those figures. You supply them, which means the answer is only as good as the inputs, and getting the inputs is most of the work. Where to find them is covered below.
Enter your details
Before you enter figures
- Home energy comes from your bills: annual kWh of electricity and gas, multiplied by the current published conversion factors.
- Travel comes from mileage by mode. Car, rail, bus and air all have very different factors per passenger mile.
- The government publishes greenhouse gas conversion factors annually, and they change as the electricity grid decarbonises.
- Full footprint calculators from established organisations do this derivation for you and are more reliable than assembling it by hand.
Published national figures vary depending on what they count. A territorial figure counts emissions produced within the UK; a consumption-based figure adds the emissions embodied in imported goods and subtracts exports, and is substantially higher. Comparing a personal estimate against a national average requires knowing which basis the average uses.
How this calculator works
A sum of three components:
Annual total = home energy + travel + other
All figures in kilograms of CO₂ or CO₂ equivalentThe estimator deliberately holds no conversion factors. Emissions factors change every year — the electricity factor in particular has fallen substantially as generation has shifted — and a hard-coded figure would silently go stale. Taking current factors from the annual government publication keeps the arithmetic honest.
Make sure all three figures use the same basis. Mixing CO₂ with CO₂ equivalent, which includes other greenhouse gases, produces a total that means neither.
Worked example: three components
Using the default figures — 2,500 kg from home energy, 1,800 from travel, 900 from other:
- Annual total: 5,200 kg CO₂, or 5.2 tonnes
Home energy is nearly half the total here, which is typical for a UK household and points to where reductions have most effect: insulation, heating controls and heating system choice. Travel at 1,800 kg is roughly what a moderate amount of car use produces — and a single long-haul return flight can exceed that on its own, which is worth knowing before optimising anything else.
Common mistakes
- Using outdated conversion factors. They change annually, particularly for electricity.
- Mixing CO₂ and CO₂ equivalent. The two are not interchangeable.
- Comparing against an average on a different basis. Territorial and consumption figures differ substantially.
- Optimising small components. Home heating and flights usually dominate everything else.
- Treating an estimate as a measurement. Personal footprints carry wide uncertainty.
Frequently asked questions
Where do I get conversion factors?
The UK government publishes greenhouse gas reporting conversion factors annually, covering electricity, fuels, transport modes, waste and more. They are the standard reference for UK reporting and are updated each year. Using the set for the year you are measuring keeps the figures consistent.
What usually makes up most of a household footprint?
For most UK households, home heating and energy use, then transport, then food and goods. The proportions vary enormously with circumstances — a household with an efficient home and no car has a very different profile from one with an older house and long commutes, and flying changes the picture more than almost anything else.
Is a personal footprint a useful measure?
It is useful for identifying where your own largest impacts are, which is what makes it worth calculating. Its limitations are well documented: individual footprints omit systemic emissions, and the concept has been criticised for shifting attention from structural change to personal responsibility. Both things can be true — knowing your own numbers is informative, and it is not the whole picture.
Should I use a proper calculator instead?
For a serious estimate, yes. Established footprint calculators derive the figures from your actual usage, apply current factors, and account for components this simple sum omits. This estimator is useful for combining figures you already have and for seeing the proportions between them.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — greenhouse gas reporting conversion factors and UK emissions statistics
- Met Office — UK climate science and observed change
Sources are checked at publication and can change — how I choose and check references.