Euro emissions standards: Euro 4, 5 and 6 explained
What the Euro emissions standards limit, when Euro 5, 6 and 6d became compulsory for new cars, how to find a car's standard and why clean air zones use it.
Updated
Euro emissions standards are the limits on exhaust pollution that a new car has to meet before it can be sold. Each stage, from Euro 1 to Euro 6, set tighter limits than the last. For a used car buyer they matter for one practical reason: clean air zones and London's ULEZ use them to decide who pays. A petrol car needs Euro 4 or newer and a diesel needs Euro 6 or newer. This guide explains what the standards limit, when the later stages became compulsory and how to find the standard of the car you are looking at.
What the standards limit
The Euro standards cap the main air pollutants in a car's exhaust, measured in milligrams per kilometre. Regulation (EC) No 715/2007, the law behind Euro 5 and Euro 6, sets limits for:
- Carbon monoxide (CO), a poisonous gas from incomplete burning of fuel.
- Hydrocarbons (HC), unburnt fuel.
- Nitrogen oxides (NOx), the gases that diesel engines in particular produce and that clean air zones target.
- Particulate matter (PM), the soot that diesel particulate filters trap.
Carbon dioxide is not one of them. CO2 is about fuel use and climate, and it is what UK car tax is based on. Euro standards are about local air quality. A car can have low CO2 and still fall below the zone standard, and the other way round.
Euro 5 and Euro 6 limits compared
The rules for Euro 5 and Euro 6 are set out in Regulation (EC) No 715/2007, which was kept in the law of Great Britain. These are the Annex I limits for passenger cars, in milligrams per kilometre.
| Pollutant | Petrol, Euro 5 | Petrol, Euro 6 | Diesel, Euro 5 | Diesel, Euro 6 |
|---|---|---|---|---|
| Carbon monoxide | 1,000 | 1,000 | 500 | 500 |
| Total hydrocarbons | 100 | 100 | not set | not set |
| Non-methane hydrocarbons | 68 | 68 | not set | not set |
| Nitrogen oxides | 60 | 60 | 180 | 80 |
| Hydrocarbons plus NOx | not set | not set | 230 | 170 |
| Particulates | 5.0, later 4.5 | 4.5 | 5.0, later 4.5 | 4.5 |
Two things stand out. First, the big change from Euro 5 to Euro 6 was for diesel NOx, which fell from 180 to 80 mg/km. Diesel NOx is what the zones focus on: TfL sets the ULEZ standard for petrol cars on NOx (Euro 4) and for diesels on NOx and particulates (Euro 6). Second, for petrol cars the particulate limit applies only to direct injection engines. The regulation brought in the 4.5 mg/km particulate limit for all new vehicles registered from 1 January 2013, before Euro 6 itself, and Euro 6 added a limit on the number of particles for direct injection petrol engines too.
Many diesels meet the Euro 6 NOx limit with selective catalytic reduction, which uses AdBlue. Our guide to AdBlue explains how that works and what goes wrong.
When each stage became compulsory
Each Euro stage had two dates: an earlier one for new models seeking type approval, and a later one after which no new car could be registered unless it complied. The later date is the one that matters most when you look at a used car's registration date.
| Stage | New models | All new cars registered |
|---|---|---|
| Euro 5 | 1 September 2009 | 1 January 2011 |
| Euro 6 | 1 September 2014 | 1 September 2015 |
| Euro 6d | not covered here | 1 January 2021 |
The Euro 5 and Euro 6 dates come from Article 10 of Regulation (EC) No 715/2007 and apply to passenger cars. Euro 1 to Euro 4 came earlier. For the purposes of a clean air zone, TfL's guide is the useful one: petrol cars that meet the ULEZ standard are generally those first registered as new after 2005, although cars that meet it have been available since 2001.
The Vehicle Certification Agency, which approves new vehicles in the UK, says Euro 6 was introduced for most new registrations in September 2015, and that since 1 January 2021 all new vehicles registered must meet Euro 6d. Euro 6d cars meet the second step of the Real Driving Emissions (RDE) requirements, which test NOx on real roads as well as in the laboratory.
There were transitional stages in between, often written as Euro 6c and Euro 6d-TEMP. For a used buyer they do not matter for the zones, because the ULEZ and clean air zone standard for diesels is Euro 6.
Where Euro 6d matters for a buyer
Euro 6d, also called RDE2, comes up in car tax. Under the GOV.UK vehicle tax rate tables, a diesel car registered on or after 1 April 2017 that does not meet the RDE2 standard pays a higher first tax payment than a petrol car with the same CO2. The first payment is made when the car is new, so this mostly affects new and nearly new cars. Our guide to car tax in 2026/27 covers what a used buyer pays.
How to find a car's Euro standard
- The V5C logbook. GOV.UK says you can find your vehicle's emission standard in the log book. Many newer logbooks show it, but not all do.
- The manufacturer. GOV.UK also points to the vehicle manufacturer. A dealer for the brand can usually confirm it from the engine and build details.
- The zone checkers. TfL's vehicle checker and the GOV.UK Drive in a clean air zone service take a registration number and tell you whether that car is charged.
The registration date is a guide, not proof. Two cars of the same model and year can have different engines and different standards. For the buying checks in full, read clean air zones and ULEZ: what to check before you buy, and use our ULEZ checker to see the zone rules.
Euro standards and the MOT
The Euro standard is what a car met when it was new. The MOT checks that it still runs cleanly enough for its age, with limits that depend on fuel and first use date. A Euro 6 car that has had its emissions equipment removed or tampered with fails the MOT and is illegal to use. Our guide to the MOT emissions test explains the test limits.
Frequently asked questions
What is the difference between Euro 5 and Euro 6?
For diesel cars, Euro 6 cut the nitrogen oxides limit from 180 to 80 mg/km and lowered the combined hydrocarbons plus NOx limit from 230 to 170 mg/km. For petrol cars the gas limits stayed the same, and Euro 6 added a particle number limit for direct injection engines.
Is a Euro 5 diesel ULEZ compliant?
No. London's ULEZ and the charging clean air zones that include cars ask diesels for Euro 6. A Euro 5 diesel pays the daily charge when it drives in those zones.
Is a Euro 4 petrol car ULEZ compliant?
Yes. Euro 4 is the minimum for petrol cars in London's ULEZ and in the charging clean air zones that include cars. Confirm the standard for the specific car with the TfL or GOV.UK checker.
How do I know if my car is Euro 6?
Check the V5C logbook, use a zone checker with the registration number, or ask the manufacturer. A diesel first registered after September 2015 is very likely to be Euro 6, but confirm it for the specific car.
Does Euro 6d mean a car is cleaner on the road?
Euro 6d cars had to meet the second step of the Real Driving Emissions requirements, which the VCA says brings on-road performance closer to the laboratory results. It is a standard for the car when new, not a measurement of any particular car today.