Decode any car hire code, from IWMR to CDAR. Learn what each letter means, what “or similar” guarantees, and what to do if you’re given the wrong car.
The four-letter code on a car hire booking, such as IWMR or CDAR, is an ACRISS code. Each letter describes one feature of the car: its size class, its body type, its gearbox and drive, and its fuel and air conditioning. “Or similar” means you’re guaranteed a car that matches that code, not the model shown in the photo.
Knowing how to read the code is the most reliable way to check what you’re actually booking. It matters most when the body style is the reason you’re hiring, as it is with estate car hire, where the same “or similar” listing can cover both a hatchback and an estate.
What Is an ACRISS Code?
ACRISS stands for the Association of Car Rental Industry Systems Standards, a body whose members include major rental companies. Its classification system grew out of the older SIPP codes created for airline booking systems, which is why you’ll still see the codes called SIPP codes on some broker sites.
The point of the system is consistency. ACRISS commissions an independent motor vehicle professional to assign codes to manufacturers’ models in Europe, the Middle East, Africa, Australia and New Zealand, so that member companies show the same code for the same car. That lets you compare an intermediate estate at one supplier with an intermediate estate at another on a like-for-like basis.
How to Read a Car Hire Code
Take IWMR, a common code in UK and European fleets:
| Position | Letter | What it describes | Meaning |
|---|---|---|---|
| 1st | I | Category (size and class) | Intermediate |
| 2nd | W | Vehicle type (body style) | Wagon/Estate |
| 3rd | M | Transmission and drive | Manual, drive unspecified |
| 4th | R | Fuel and air conditioning | Unspecified fuel, air conditioning fitted |
So IWMR is an intermediate estate with a manual gearbox and air conditioning. Change the third letter to A and you have IWAR, the automatic version. Change the second letter to D and you have IDMR, a 4-5 door hatchback or saloon in the same size class.
1st Letter: Category
The first letter sets the size and price band, based on size, cost, power and luxury. Each size has an Elite version, used for premium brands of a similar size.
| Standard | Elite version |
|---|---|
| M = Mini | N = Mini Elite |
| E = Economy | H = Economy Elite |
| C = Compact | D = Compact Elite |
| I = Intermediate | J = Intermediate Elite |
| S = Standard | R = Standard Elite |
| F = Fullsize | G = Fullsize Elite |
| P = Premium | U = Premium Elite |
| L = Luxury | W = Luxury Elite |
| O = Oversize | X = Special |
Elite means a premium badge in that size band. It doesn’t mean more space. An Intermediate Elite car is usually a similar size to an Intermediate one, just from a more upmarket brand.
Several letters appear in more than one position with different meanings. W as a first letter is Luxury Elite. W as a second letter is Wagon/Estate. Always read a letter by its position.
2nd Letter: Vehicle Type
The second letter is the body style. For most travellers it’s the most important letter on the booking, because it decides how practical the car is.
| Letter | Vehicle type | What to know |
|---|---|---|
| B | 2-3 door | Awkward for rear passengers and child seats |
| C | 2/4 door | Can be either, depending on the fleet |
| D | 4-5 door | Standard hatchback or saloon |
| W | Wagon/Estate | The estate version of a C or D car |
| V | Passenger van | 6 or more seats (see below) |
| F | SUV | 4WD or off-road ability is typical but not guaranteed |
| G | Crossover | SUV styling on a car platform, no 4WD capability |
| M | Monospace | Five-seat MPV with extra headroom |
| T | Convertible | Usually four seats |
| N | Roadster | Two seats, open roof |
| E | Coupe | Two doors, small rear seats |
| L | Limousine/Sedan | Extended luxury car, or a saloon in some markets |
| S | Sport | Sports car with a more powerful engine |
| P / Q | Pick-up | P is single or extended cab, Q is double cab |
| K | Commercial van | Cargo, not passengers |
| Z | Special offer car | Used for promotions and guaranteed models |
The W definition is the useful one to remember. ACRISS describes an estate as a derivative of a C or D type car where the second letter simply changes to W. That’s why an Octavia hatchback and an Octavia Estate can sit in the same size category with different codes, and why the code, not the model name, tells you which one you’re getting.
The F and G split matters too. Many cars people call SUVs are crossovers, and a G code tells you there’s no four-wheel drive. If you need 4WD for snow or rough roads, look for F and then check the third letter.
Passenger Vans: The First Letter Changes Meaning
When the second letter is V, the first letter stops describing size and starts describing seats:
| Code start | Seats |
|---|---|
| IV | 6+ seats |
| JV | Elite 6+ seats, or 5+2 with two fold-down seats |
| SV | 7+ seats |
| FV | 7+ seats plus more space |
| PV | 8+ seats |
| LV | 9+ seats |
| XV | 12+ seats |
| OV | 15+ seats |
If you need seven seats and room for luggage, FV is a better bet than SV. JV can mean two occasional seats in the boot, which leaves little luggage space when they’re in use.
3rd Letter: Transmission and Drive
| Manual | Automatic |
|---|---|
| M = Manual, drive unspecified | A = Automatic, drive unspecified |
| N = Manual 4WD | B = Automatic 4WD |
| C = Manual AWD | D = Automatic AWD |
If you can only drive an automatic, this is the letter to check. Automatic codes use A, or B and D for the 4WD and AWD versions. Everything else in this column is a manual. ACRISS has also added letters for self-driving levels 3 to 5, though you’re unlikely to see them on a normal booking yet.
4th Letter: Fuel and Air Conditioning
| Letter | Meaning |
|---|---|
| R | Unspecified fuel, air conditioning |
| N | Unspecified fuel, no air conditioning |
| D / Q | Diesel with / without air conditioning |
| V / Z | Petrol with / without air conditioning |
| H | Hybrid, including mild hybrids |
| I | Plug-in hybrid |
| E / C | Battery electric |
| L / S | LPG or compressed gas with / without air conditioning |
R is by far the most common fourth letter, and it tells you less than people assume. It confirms air conditioning but not the fuel, so an R car could be petrol or diesel. If fuel type matters to you, for running costs on a long trip or because you’d rather avoid diesel, check the booking details or ask the supplier.
An I code (plug-in hybrid) or E/C code (fully electric) deserves a second look before you book. You’ll need access to charging to get the benefit, and on estates in particular, plug-in hybrid batteries can take a noticeable chunk out of boot space.
Common Car Hire Codes Decoded
| Code | Meaning |
|---|---|
| ECMR | Economy, 2/4 door, manual, air con |
| CDMR | Compact, 4-5 door, manual, air con |
| CDAR | Compact, 4-5 door, automatic, air con |
| IDMR | Intermediate, 4-5 door, manual, air con |
| IWMR | Intermediate estate, manual, air con |
| IWAR | Intermediate estate, automatic, air con |
| SWAR | Standard estate, automatic, air con |
| IFAR | Intermediate SUV, automatic, air con |
| IGAR | Intermediate crossover, automatic, air con |
| FVAR | 7+ seat passenger van with extra space, automatic, air con |
| CDAE | Compact, 4-5 door, automatic, electric |
What “Or Similar” Actually Guarantees
Rental companies sell categories, not models. The car in the listing photo is an example of the category. Sixt’s guidance, for instance, states that the ACRISS code shows the vehicle class rather than a guaranteed model, and that customers will get a car from the same category or a higher one.
In practice, “or similar” should give you a car that matches every letter of the code you booked. What it doesn’t cover is anything outside the code:
- The make and model. You can request a model, but the branch doesn’t have to provide it.
- The exact boot size. Cars within one category can differ noticeably in boot space.
- Petrol or diesel, if the fourth letter is R.
- Extras such as a tow bar, roof bars, child seats or built-in sat nav, unless booked separately.
The biggest trap is a listing that shows a model name without a code. Enterprise UK, for example, lists its intermediate class as “Skoda Octavia or similar”. The Octavia is sold as both a hatchback and an estate, so the name alone doesn’t tell you which body you’ll get. If you need an estate, look for W in the second position, or for the words estate, wagon, Touring, Avant or SW in the listing.
The one exception is a guaranteed model offer. ACRISS reserves Z in the second position for promotions and guaranteed models, so a Z code can mean you get exactly what’s pictured. Read the offer terms, though, because suppliers use Z in different ways, as the next section explains.
Not Every Supplier Uses the Codes the Same Way
ACRISS codes are a standard, but suppliers can adapt them, and some do. Sixt publishes its own version of the table and marks the entries that are Sixt-specific. A few differences from the official ACRISS matrix:
| Position and letter | Official ACRISS meaning | Sixt’s usage |
|---|---|---|
| 2nd letter Z | Special offer car, including guaranteed models | “Lucky dip” vehicle |
| 3rd letter D | Automatic, all-wheel drive | 4-wheel drive, automatic |
| 4th letter H | Hybrid | Plug-in hybrid |
| 4th letter V | Petrol with air con | 5+2 seat vehicle |
The Z difference is the one to watch: at one supplier it can mean a guaranteed model, at another the opposite. Sixt also sorts cars into size categories by length and boot volume, which may not line up exactly with another supplier’s grouping.
Comparison and broker sites add another layer. Some show the full code, some show only a category name like “Intermediate Estate”, and some show only a model name. When the code and the description disagree, trust neither. Check the supplier’s own terms or ask before you pay.
What to Do If You’re Given a Different Car
Fleets move quickly. Late returns and cleaning delays mean the branch may not have your exact category when you arrive, especially in school holidays. If the car on offer doesn’t match your booking:
- Compare the code on the rental agreement with your booking confirmation before you sign. The agreement should show the category of the car you’re actually getting.
- Ask for a car that matches the code, or a free upgrade. A higher category at no extra cost is the normal solution when your class has run out.
- Don’t accept a lower category without a price adjustment. An intermediate hatchback isn’t a substitute for an intermediate estate if your luggage won’t fit. Load your bags before you leave if you’re unsure.
- Check what changes with an upgrade. A bigger car can come with a larger security deposit or higher fuel costs. Get any change confirmed in writing before you drive away, because it’s much harder to dispute afterwards.
If no suitable car is available at all, Which? advises that you can hold the company in breach of contract. For complaints about a UK rental, the BVRLA runs a government-approved alternative dispute resolution service for its members, which include large operators such as Hertz and Avis. You’ll need to complete the company’s own complaints process first. For cross-border rentals within Europe, the European Car Rental Conciliation Service handles disputes involving its member companies. If you paid by credit card, a Section 75 claim is another route.
Using Codes to Book the Right Car
- Start with the second letter. Decide the body style you need, whether W for luggage or V for seats, before you compare prices.
- Then check the third letter if you need an automatic or four-wheel drive. Automatics sell out first at busy periods.
- Compare codes, not names. “Intermediate” at one supplier and “Intermediate” at another are only comparable if the full codes match.
- Screenshot the booking page showing the code and description. It’s your evidence if the car at the desk doesn’t match.
Car Hire Codes: FAQs
Are ACRISS codes and SIPP codes the same thing?
Essentially, yes. ACRISS codes are based on the original SIPP codes used in airline booking systems, expanded over the years to cover new vehicle types and fuels.
Which letter tells me if the car is automatic?
The third letter. A means automatic, and B and D are automatic 4WD and AWD. M means manual.
How do I know if a hire car is an estate?
Look for W as the second letter of the code. A model name like “Skoda Octavia or similar” on its own doesn’t confirm the estate body.
Does the code tell me if the car is petrol or diesel?
Only sometimes. D means diesel and V means petrol, but most hire cars carry R, which confirms air conditioning without specifying the fuel.
Can I refuse a car that doesn’t match my booking?
Yes, if it’s in a different category from the one you booked. Ask for a matching car or a free upgrade, and don’t drive away in a lower category without a price adjustment agreed in writing.
What does Elite mean in a car hire category?
A premium brand within the same size band. Intermediate Elite (J) is typically a similar size to Intermediate (I), with a more upmarket badge rather than more space.
How This Guide Was Researched
Code definitions come directly from the ACRISS classification matrix, car type definitions and fuel type guide. Supplier variations were checked against Sixt’s published ACRISS guide, and fleet naming against Enterprise UK’s vehicle listings. Consumer rights information comes from Which?, the BVRLA, GOV.UK and the ACRISS rental FAQs. ACRISS updates its matrix as new vehicle types appear, so we review this guide at least [every six months].