A car's CO2 emissions figure affects how much you pay in road tax, whether you're charged in Clean Air Zones like ULEZ, and how much the vehicle costs to run. Yet most car owners have never looked up the number.
Here's how to check it and what it means in practice.
How to check your car's CO2 emissions
The quickest way is to enter your registration number on our free car check. You'll see the CO2 emissions figure (in g/km) recorded against your vehicle by the DVLA, along with the fuel type, engine size, and Euro emission standard.
You can also find the figure:
- On the V5C logbook — The CO2 emissions are listed on the vehicle registration certificate.
- On the VCA (Vehicle Certification Agency) website — The official UK type approval database, which lists emissions for every approved vehicle.
- In the owner's manual — Usually in the technical specifications section.
Our free check is the fastest method — it takes seconds, shows you the official DVLA figure, and gives you the full vehicle specification at the same time.
Why CO2 emissions matter
Road tax (VED)
CO2 emissions are the main factor in calculating Vehicle Excise Duty for most cars. For the complete 2026 car tax rates broken down by band, see our dedicated guide. The system works differently depending on when your car was first registered:
Registered from 1 April 2017 onwards:
- First year tax is based on CO2 emissions — ranging from £0 for zero-emission vehicles to over £2,000 for the highest emitters
- After the first year, most cars pay a flat standard rate (currently £190/year)
- Cars with a list price over £40,000 pay an additional £410/year supplement for 5 years
Registered before 1 April 2017:
- Tax is based entirely on CO2 emissions bands (A to M)
- Band A (up to 100 g/km): £0
- Higher bands pay progressively more, up to over £600/year for Band M
You can see your vehicle's current tax status and what you're paying using our tax check.
ULEZ and Clean Air Zones
While ULEZ charges are based on the Euro emission standard (Euro 4 for petrol, Euro 6 for diesel) rather than CO2 directly, the two are related. Lower-CO2 vehicles tend to be newer and more likely to meet the required Euro standard.
Check your vehicle's ULEZ compliance alongside its CO2 figure to get the full emissions picture.
Fuel costs
CO2 emissions are directly linked to fuel consumption. A car emitting 100 g/km of CO2 will use roughly half the fuel of one emitting 200 g/km over the same distance. When comparing vehicles, the CO2 figure is a useful proxy for real-world fuel economy.
That said, official test figures (particularly the older NEDC test cycle) often understate real-world consumption. The newer WLTP test cycle is more realistic, but still expect to use 10–20% more fuel than the official figure in everyday driving.
Company car tax (BIK)
If you have a company car, the CO2 emissions figure directly determines your Benefit in Kind (BIK) tax rate. Lower emissions mean a lower percentage of the car's list price is treated as taxable income. This is why electric and plug-in hybrid vehicles are popular as company cars — the BIK rates are significantly lower.
Understanding the numbers
CO2 emissions are measured in grams per kilometre (g/km). Here's a rough guide to what the figures mean:
| CO2 (g/km) | Category | Typical vehicles |
|---|---|---|
| 0 | Zero emission | Battery electric, hydrogen |
| 1–50 | Ultra-low | Plug-in hybrids (PHEV) |
| 51–100 | Low | Small efficient petrol/diesel, mild hybrids |
| 101–130 | Below average | Average family cars, smaller SUVs |
| 131–160 | Average | Mid-size petrol cars, small SUVs |
| 161–200 | Above average | Larger petrol cars, SUVs, performance cars |
| 200+ | High | Large SUVs, sports cars, older diesels |
The UK average for new cars sold in 2025 was around 120 g/km, pulled down by the increasing proportion of electric and hybrid vehicles in the mix.
NEDC vs WLTP — which figure do I have?
If your car was type-approved before September 2018, the CO2 figure on its records will be based on the NEDC (New European Driving Cycle) test. Cars approved from September 2018 use the WLTP (Worldwide Harmonised Light Vehicle Test Procedure).
The key difference:
- NEDC figures are lower — The test was conducted in a laboratory with unrealistic driving conditions, producing optimistic results
- WLTP figures are more realistic — The test includes higher speeds, longer distances, and real-world driving patterns
A car that was rated at 120 g/km under NEDC might show 140–150 g/km under WLTP for identical real-world performance. This matters when comparing cars of different ages — the numbers aren't directly comparable across the two test cycles.
For road tax purposes, cars are assessed using whichever test was applicable when they were type-approved. The DVLA records the correct figure for your vehicle's tax band.
How to reduce your emissions (and costs)
If your current car has high CO2 emissions and you're looking to reduce costs:
- Consider your next car carefully — Use our free car check to compare CO2 figures across different vehicles you're considering
- Check the road tax impact — Higher CO2 means higher VED. See what you'd save with our tax check
- Factor in ULEZ — If you drive in London or other Clean Air Zones, a high-CO2 vehicle may also mean daily charges. Check with our ULEZ check
- Drive efficiently — Smooth acceleration, maintaining steady speeds, keeping tyres properly inflated, and removing unnecessary weight all reduce real-world emissions and fuel consumption
- Keep up with maintenance — A well-serviced engine runs more efficiently. Check your MOT history for any advisories related to emissions or the exhaust system
The bottom line
Your car's CO2 emissions figure is more than a technical statistic — it directly affects what you pay in road tax, whether you face Clean Air Zone charges, how much you spend on fuel, and (for company cars) your tax bill.
Check yours in seconds with a free car check. Enter any UK registration number to see the CO2 figure alongside the full vehicle specification, MOT history, tax status, and ULEZ compliance — all in one place, with no signup required.