What Tyre Size Fits My Car? How to Find, Read & Check Yours

The fastest honest answer to "what tyre size fits my car" is that the size is printed on the car itself. No website table can know your trim, your wheel option or what a previous owner changed, so this guide shows you the three places to find your size, how to read the code once you have it, what to do when the sources disagree, and how to judge an alternative size. By the end you will have the full marking — size, load index and speed rating — written down and ready to order.

This is a calculation, not a safety approval. Always check your vehicle's door-jamb placard, load index and speed rating, and confirm fitment with a tyre professional before fitting a different tyre size.

what tyre size fits my car: The three places your tyre size is recorded

The first and most important place is the door-jamb placard. Open the driver's door and look at the frame around the opening: on most cars a sticker there lists the original tyre size for the front and rear axles, the load index, the speed rating and the recommended cold pressures, sometimes with different pressures for light and full loads. If the driver's jamb is bare, check the passenger door jamb, the inside of the fuel filler flap and the glovebox — manufacturers put it in different places, but it is always somewhere accessible without tools. The placard is the manufacturer's statement of what the car was built with, and every other check is measured against it.

The second place is the owner's manual. The manual lists the approved tyre sizes for the car, often in a small table by trim or wheel option, and it explains the pressures and the load and speed requirements in full sentences rather than the placard's shorthand. If the manual is missing — common with used cars — the manufacturer's website usually offers a free download by model and year. The third place is the sidewall of the tyre currently fitted. The size is moulded into the rubber in large characters, and reading it takes seconds. But the fitted tyre is only evidence of what is on the car now. A previous owner may have fitted an alternative size, so the sidewall tells you what to replace, not necessarily what the car was designed for.

Check at least two of the three sources. If the placard and the sidewall agree, you have your answer. If they disagree, the placard wins, and the difference needs investigating before you order — work out the diameter change with the tyre size calculator and ask a tyre professional whether the fitted size is a suitable alternative. A dealer can also look up the original specification from the VIN if the placard is damaged or unreadable.

How to read the size code for what tyre size fits my car

A size code describes the tyre's dimensions in three numbers. Take 205/55R16 as a worked example: the first number, 205, is the section width in millimetres; the second, 55, is the aspect ratio, so the sidewall is 112.8 mm tall; the R stands for radial construction; and the final number, 16, is the rim diameter in inches. The overall diameter is 631.9 mm, the circumference is 1985.2 mm, and the tyre turns 810.7 times per mile. These are nominal new-tyre dimensions — real tyres vary slightly by brand, model, wear and inflation pressure.

After the size code come the load index and the speed rating. The load index is a number corresponding to the maximum weight each tyre can carry, and the speed rating is a letter corresponding to the maximum speed it is designed to sustain. Both must meet or exceed the figures on the placard. A tyre in the right size with a lower load index than the placard asks for is not a like-for-like replacement. See the full size page for 205/55R16 tyre size and the tyre load index calculator and tyre speed rating calculator for the full scales.

what tyre size fits my car: What to do when the placard and the fitted tyre disagree

A disagreement between the placard and the fitted tyre is common and not automatically a problem — but it is a question, not something to ignore. First, write down both sizes in full, including load index and speed rating. Then look up both diameters and work out the percentage difference: divide the fitted diameter by the placard diameter, subtract 1 and multiply by 100. If the result is within ±3%, the speedometer effect is small, though that alone does not make the size right for the car. Check the load index and speed rating against the placard, check the clearance at the arches and suspension, and check whether the spare still matches. If the difference is larger than ±3%, or the ratings fall short, treat the fitted size as a mistake to correct rather than a size to repeat, and ask a tyre professional to confirm before you buy. The tyre size comparison tool and the speedometer error calculator run the numbers for any pair.

what tyre size fits my car: Choosing an alternative size

Sometimes a different size is a deliberate choice: a wider tyre for grip, a taller sidewall for comfort, or a plus-size wheel change. The commonly used guideline is to stay within ±3% of the original diameter, which keeps the speedometer error small and the gearing close to the design intent. It is a guideline, not a safety approval, and it says nothing about clearance, wheel width or load rating. Work the numbers first, then confirm the physical fit on the car. A different size also needs its own pressure — the placard pressure was set for the original size — so check the tyre maker's guidance and the placard rather than carrying the old pressure across. Buy in axle pairs at least, and keep the receipt and the size details for the next change.

what tyre size fits my car: Common mistakes

The most common mistake is ordering by model and year alone: the same model year can wear different sizes across trims and wheel options. The second is copying the fitted tyre without checking the placard. The third is ignoring the load index and speed rating and choosing on size and price alone. The fourth is using the maximum pressure on the sidewall instead of the placard pressure. The fifth is fitting different sizes across an axle, which affects handling and can confuse stability systems. And the sixth is assuming a size fits because the diameter is within ±3% — that rule is about the speedometer, not about physical clearance, and only a check on the car settles that.

Frequently asked questions

Where is the tyre size placard on my car?

On most cars the tyre size placard is on the driver's door jamb, visible when the driver's door is open. If it is not there, check the passenger door jamb, the inside of the fuel filler flap, the glovebox, or the owner's manual. It lists the original size, load index, speed rating and cold pressures.

How do I read the tyre size code?

Take a code like 205/55R16 for a tyre: 205 is the width in millimetres, 55 is the aspect ratio (sidewall height as a percentage of the width), R means radial construction, and 16 is the rim diameter in inches. The numbers and letters after that are the load index and speed rating.

For what tyre size fits my car, can I fit a different tyre size from the one on the placard?

You can consider an alternative within ±3% of the original diameter as a starting point, but that is only a guideline for the speedometer. Clearance, wheel width, load index and speed rating all have to be checked on your car and confirmed with a tyre professional before fitting.

What if my placard and my fitted tyre show different sizes for what tyre size fits my car?

Trust the placard for what the car was built with. Work out the diameter difference between the two sizes, check the load index and speed rating against the placard, and ask a tyre professional whether the fitted size is a suitable alternative before repeating it.

Do I need the load index and speed rating, or just the size for what tyre size fits my car?

You need all three. The load index and speed rating must meet or exceed the placard figures. A tyre in the right size with a lower load index than specified is not a like-for-like replacement, whatever the price.

What tyre pressure should I use?

Use the cold pressures on the door-jamb placard for the size fitted, not the maximum pressure moulded into the tyre sidewall. Check pressures monthly when the tyres are cold, and use the higher placard figure when the car is fully loaded if the placard lists one.