To find my tire size, I can read the code molded into a tire’s sidewall—but that tells me only what is currently installed, not whether it is the correct fit for my vehicle. First, record the complete size and service markings. Then compare them with the tire information placard on the vehicle and the owner’s manual, paying attention to different front and rear sizes, load requirements, and approved alternatives. If the current tires disagree with the vehicle’s specifications, don’t assume the sidewall is right. Confirm the correct fitment before ordering so the replacement matches the vehicle’s requirements as well as the wheel.
Park on level ground and look at the outer sidewall of each tire. The size is usually molded into the rubber as a sequence of letters and numbers. It may appear beside the tire brand and model, and it can be repeated elsewhere on the sidewall. Clean off dirt if needed, and copy the entire code rather than just the first group of numbers.
A common passenger-tire marking looks like P225/65R17 102H. The elements describe different specifications:
| Marking | What it means | What to check |
|---|---|---|
| P | A tire classification used on some passenger tires | Other tires may use an LT prefix or have no prefix. Record what is shown. |
| 225 | Nominal section width in millimeters | This is the tire’s width specification, not the width of the wheel. |
| 65 | Aspect ratio: sidewall height as a percentage of section width | A different ratio can change the tire’s overall dimensions. |
| R | Radial construction | Here, R does not mean the tire’s radius. |
| 17 | Wheel diameter in inches | The tire must be made for the wheel diameter it will mount on. |
| 102H | Load index and speed symbol | These are service ratings, not part of the width-and-diameter size alone. |
In this example, the 65 aspect ratio means the sidewall height is nominally 65% of the tire’s section width. The 17 refers to the diameter of the wheel that the tire fits—not the tire’s overall diameter. The load index, 102, corresponds to a load capacity under specified conditions; it is not a weight in pounds. The H speed symbol is a separate service rating. When replacing a tire, match the size and meet the vehicle maker’s requirements for load and speed ratings.
Some tires include additional markings such as XL or Extra Load, indicating a higher-load version within the tire’s specification. Light-truck tires may begin with LT and use different load and pressure conventions. Don’t compare tires by size digits alone; confirm that the full tire type and service description are suitable for the vehicle.
Use the vehicle’s tire placard as the main reference for its original tire specifications. It is commonly found on the driver’s door jamb or door edge, though the location can vary. The owner’s manual may also list the correct sizes, including separate fitments for different trims, wheel packages, or front and rear axles.
The placard can list both tire size and recommended cold inflation pressure. Those details serve different purposes: the size identifies the tire specification, while the pressure is the vehicle maker’s recommended inflation level for normal use. Don’t use the maximum pressure molded into a tire’s sidewall as a substitute for the vehicle’s recommended pressure.
| Where to look | What it can confirm | What to keep in mind |
|---|---|---|
| Current tire sidewall | The size and service markings of the tire installed now | It may be an incorrect replacement or one of several approved options. |
| Vehicle tire placard | Vehicle-specific tire information and recommended cold pressure | Check whether it lists different front and rear sizes. |
| Owner’s manual | Additional specifications and guidance for the vehicle | Make sure the information applies to the vehicle’s trim and wheel setup. |
| Vehicle manufacturer or dealer | Help identifying the correct specification when records are unclear | Provide the exact model, year, trim, and relevant wheel details. |
Compare the sidewall with the placard instead of relying on either one in isolation. If they match and the tires are the same size on all four corners, you have a useful starting point. If they differ, or the placard lists more than one size, look up the vehicle’s approved fitments before buying. A vehicle may have a staggered setup, with one size for the front axle and another for the rear. In that case, replacing all four tires with one size could be wrong even if that size appears on one of the sidewalls.
A tire can share the same wheel diameter as the original and still be an unsuitable replacement. Width and aspect ratio affect the tire’s overall dimensions, while load capacity and tire construction affect whether it meets the vehicle’s requirements. Fitment also depends on the wheel itself and the space available around the suspension, brakes, and bodywork.
Before choosing a size other than the one shown on the placard, confirm that the alternative is approved for the exact vehicle and wheel configuration. A tire retailer’s vehicle selector can help narrow the choices, but confirm the result against the manual, placard, or vehicle manufacturer when details don’t agree. A make-and-model match alone may not account for every trim or optional wheel package.
Changing to a different overall tire size can affect clearance, handling, and the relationship between road speed and the vehicle’s speedometer reading. It may also interfere with systems that rely on wheel-speed information. The exact effects depend on the vehicle and the change, so don’t treat an online size calculator or a general “plus-sizing” rule as approval. Confirm the proposed combination with a qualified tire professional or the vehicle manufacturer.
Pause before buying. The tire that is currently installed might be a valid alternate size, but it might also be an unsuitable replacement from a previous owner or repair. The placard and manual provide a stronger basis for identifying the vehicle’s intended fitment than simply copying an unfamiliar sidewall code.
If a tire is too worn or damaged to read, inspect another tire on the vehicle, but treat that as a clue rather than final confirmation. Check the placard and manual as well. If the vehicle has been modified or the specifications are missing, get the wheel and vehicle fitment identified by a tire professional instead of guessing from a partial marking.
Vehicle details can help a tire retailer or manufacturer identify likely fitments, but the result may depend on trim, wheel package, and front-to-rear configuration. Confirm the recommendation with the tire placard or owner’s manual before ordering.
No. The size code identifies tire dimensions and, alongside other markings, service information. Use the vehicle’s tire placard or manual for the recommended cold inflation pressure, unless the manufacturer provides different instructions for your situation.
Only if the alternative is approved for your vehicle and wheel setup. A size change can affect clearance, handling, and vehicle readings, and it must still meet the required load and speed specifications. Confirm the complete fitment before buying.
Not always. Some vehicles use different sizes on the front and rear axles, so check the placard and manual. If the vehicle uses all-wheel drive, follow its manufacturer’s guidance on tire-size and tread-depth differences when replacing fewer than four tires.
Not necessarily. A tire includes several markings for size, load, speed, manufacturing, and other specifications. Find the complete size sequence, such as 225/65R17, then check the nearby service markings separately.
To find my tire size accurately, I should read the full sidewall code and verify it against the vehicle’s placard and manual. Before buying, I also need to confirm the load and speed ratings, wheel fit, and any front-to-rear differences. If the markings conflict or the vehicle has been modified, have the fitment confirmed rather than guessing.
