What does tCO2e mean?

tCO2e stands for tonnes of carbon dioxide equivalent. It’s the standard unit for measuring a carbon footprint, and it adds every greenhouse gas together into one number by converting each into the amount of carbon dioxide that would cause the same warming. One tCO2e is 1,000 kg of CO2e, or roughly the emissions from burning 480 litres of petrol.

You’ll see it on supplier questionnaires, grant forms and tender documents, usually as “please state your total emissions in tCO2e”. Here’s what it means and how to work yours out.

What does the “e” in CO2e mean?

The “e” stands for equivalent. Businesses don’t only emit carbon dioxide. Burning gas and fuel also releases small amounts of methane and nitrous oxide. Landfill sites release methane. Air conditioning can leak refrigerant gases thousands of times more potent than CO2.

To add these together, each gas is multiplied by its global warming potential (GWP), which measures how much warming it causes over 100 years compared with the same mass of carbon dioxide. The UK government conversion factors mainly use the values from the IPCC’s Fifth Assessment Report, including:

• Carbon dioxide: 1
• Methane: 28
• Nitrous oxide: 265

So one kilogram of methane counts as 28 kilograms of CO2e. Add everything up and you have a single tCO2e figure that anyone can compare.

How big is one tonne of CO2e?

Abstract numbers are hard to picture, so here’s what one tonne looks like using rounded 2026 UK government factors. These are approximate:

• About 7,600 kWh of grid electricity
• About 5,500 kWh of gas for heating
• About 480 litres of petrol
• About 3,800 miles in an average petrol car
• About 25 return train trips between London and Edinburgh
• A little less than one return economy flight from London to New York, which comes to around 1.3 tCO2e

That last comparison surprises most people. A single long-haul trip can outweigh a year of office electricity.

kgCO2e, tCO2e and other units you might see

The same idea comes in different sizes:

Unit	Means	Where you’ll see it
gCO2e	grams	Per kWh or per km on energy and travel sites
kgCO2e	kilograms	UK conversion factors, individual line items
tCO2e	tonnes (1,000 kg)	Business footprints, supplier forms, tenders
MtCO2e	million tonnes	National and large company figures

The DEFRA conversion factors are given in kgCO2e per unit, so you’ll do your sums in kilograms and divide by 1,000 at the end.

How is tCO2e calculated?

Every line of a carbon footprint follows the same formula:

Activity × conversion factor = kgCO2e

For example, a business using 9,000 kWh of electricity in 2026 would multiply by roughly 0.131 kg per kWh to get about 1,180 kgCO2e, or 1.18 tCO2e. Do the same for gas, vehicles, travel, waste and water, add them together, and you have your total.

The conversion factor already includes the other greenhouse gases, so you don’t need to handle methane or nitrous oxide separately. Our guide on how to calculate your small business carbon footprint walks through a full worked example.

Is tCO2e the same as tCO2?

Not quite. tCO2 counts only carbon dioxide. tCO2e includes every greenhouse gas converted to its CO2 equivalent.

For burning gas or diesel, the difference is tiny, because almost all the warming comes from carbon dioxide. For other sources, it’s large. Commercial waste sent to landfill, for instance, has a factor of roughly 520 kg CO2e per tonne, almost all of it from methane released as the waste breaks down. Report in tCO2e unless someone specifically asks for CO2 only.

What is a normal tCO2e figure for a small business?

There isn’t a single typical number, because a co-working freelancer and a bakery with two delivery vans are very different businesses. From the worked examples in our guides, using approximate 2026 factors:

• A freelancer with one co-working desk three days a week: around 0.25 tCO2e for the desk
• A six-person agency in a gas-heated office with some travel: around 5 tCO2e
• A 12-person consultancy with two diesel vans: around 14 tCO2e

Because size varies so much, many buyers also ask for an intensity figure, such as tCO2e per employee or per £1 million of turnover. That lets them compare suppliers of different sizes fairly, and it lets you show progress as you grow.

Why do people ask for tCO2e instead of kWh or miles?

Because it’s the only unit that lets them add different activities together. Your customer can’t sum your kWh of electricity, your litres of diesel and your flights to Frankfurt. They can sum tonnes of CO2e, and then add your figure to the hundreds of other suppliers in their own Scope 3 total.

It also travels well. A tonne of CO2e means the same thing in a council grant form, an investor’s due diligence questionnaire and an EU customer’s VSME request, so one well-documented calculation can answer all of them.

That said, keep your activity data. kWh, litres and kilometres are what you actually control, and they’re what you’ll use to show progress when conversion factors change from year to year.

What are the common mistakes with tCO2e?

A few come up again and again on supplier forms:

• Mixing kilograms and tonnes. A figure of 5,100 entered in a box asking for tCO2e makes a six-person agency look like a factory. Check the unit twice.
• Using an old factor year. Electricity factors in particular change a lot. The 2026 UK grid factor is about 26% lower than 2025.
• Leaving out the method. A number with no explanation is hard to trust. One line on scopes covered and factors used fixes that.
• Netting off offsets. If you buy carbon credits, report them separately. Your footprint is what you emitted, before any offsetting.

Where will you be asked for tCO2e?

Most often in:

• Supplier questionnaires from larger customers measuring their Scope 3 emissions
• Grant applications, especially council decarbonisation grants that ask for current emissions and estimated savings
• Carbon Reduction Plans for central government contracts under PPN 006
• Green loan applications and bank sustainability questions

In each case, a total in tCO2e, a split by scope and a short note on your method is usually enough.

The ESG Now report gives you your total in tCO2e, broken down by scope and by source, with every calculation shown. It covers heating fuels, company vehicles, refrigerants, electricity, EV charging, water, waste, deliveries, business travel, commuting and homeworking. Most small businesses finish in under 30 minutes. Start your free report, or read about supplier questionnaires if that’s what brought you here.