A car's tyre size is never hard to find; it is recorded in several places, and they should all agree. The four reliable sources are the tyre sidewall, the door placard, the handbook and, in the UK, a registration lookup.
On the tyre sidewall
The most direct source is the tyre already fitted. The full size, such as 205/55 R16 91V, is moulded into the outer sidewall in raised lettering, usually standing out clearly once it is wiped clean. Checking the sidewall confirms exactly what is on the car right now, which is useful when ordering a matching replacement.
The one caution is that a previously fitted tyre might not be the car maker's recommended size, if it was changed at some point. For that reason the sidewall is best confirmed against the door placard.
While reading the sidewall, small coloured paint dots may also be visible on a newer tyre. These are fitting references used when the tyre was mounted rather than part of the size.
On the door placard
The definitive reference is the placard fitted by the car maker. It is most often found on the edge of the driver's door or on the door frame the door closes against, and on some cars on the fuel filler flap or inside the glovebox. It lists the recommended tyre sizes, the correct pressures, and frequently the load index and speed rating as well.
Because the placard shows the specification the car was designed and approved around, it is the size to trust if anything else disagrees. Many cars also list a different front and rear pressure here, and sometimes a separate figure for a fully loaded car.
In the handbook
The car's handbook carries the same recommended sizes and pressures as the placard, often with extra detail such as optional wheel-and-tyre combinations and the space-saver spare. It is the natural place to check when the placard is missing or hard to read.
By registration, in the UK
In the UK, most tyre retailers offer a registration lookup: on Tyres.co.uk, for example, a number plate brings up the standard sizes for the car. It is the quickest route when the car is not to hand, and it is how online tyre ordering usually starts.
It does have a limit. A lookup returns the standard fitment for that model, so a car running non-standard wheels, or one of several factory options, may not match exactly. Where that is a possibility, the sidewall and door placard settle it.
When the sources disagree
If the fitted tyre, the placard and a registration lookup do not all match, the door placard wins, because it reflects how the car left the factory. A mismatch usually means the wheels or tyres were changed at some point. When the right choice is not obvious, fitting the placard size or checking with a fitter is the safe course.
From the workshop: nine times out of ten the door placard answers everything, size, pressures, the lot. The trouble starts when someone has fitted aftermarket wheels and the tyre on the car no longer matches the plate lookup. Then we go back to the placard and work from there.
Common questions
Where do I find my car's tyre size?+
Four places: moulded on the tyre sidewall, on the placard inside the driver's door, in the car's handbook, and, in the UK, by entering the registration on most tyre retailers' websites. The door placard shows the car maker's recommended size.
Where is the tyre placard on a car?+
Usually on the edge of the driver's door or the door frame it closes against. On some cars it is on the fuel filler flap or inside the glovebox. It lists the recommended tyre sizes and pressures.
Can I find my tyre size by registration?+
In the UK, most tyre retailers let you enter a number plate to return the standard tyre sizes for that vehicle. It is convenient, but a car with non-standard wheels may differ, so the sidewall and door placard remain the definitive check.
What if the tyre on my car is a different size to the door placard?+
The door placard shows the size the car was designed and approved around, so it is the safe reference. A fitted tyre that differs may have been changed at some point; if in doubt, fit the placard size or take advice from a fitter.