Tire size explained begins with a code on the sidewall, but the wheel diameter is only one part of it. A marking such as P215/65R16 95H gives information about the tire’s width, sidewall height, construction, wheel fitment, load index and speed rating. Before replacing a tire, compare the complete specification with the vehicle’s tire placard or owner’s manual. The correct replacement must suit the wheel and vehicle, not merely look close in size. A mismatch can affect clearance, handling, ride comfort and the readings of vehicle systems.
Consider the example P215/65R16 95H. The code is read from left to right. The first part describes the tire’s size and construction; the final characters are its service description. Some tires omit the initial “P,” and markings can vary by sizing system and market, so don’t assume every tire will use exactly this format.
| Marking | What it means | What to check |
|---|---|---|
| P | Identifies a P-metric passenger tire. | Confirm the tire type matches the vehicle’s approved fitment. |
| 215 | Nominal section width in millimetres. | This is not necessarily the tread width; actual dimensions can vary by tire model and rim. |
| 65 | Aspect ratio: the sidewall height is 65% of the nominal width. | A smaller number generally means a shorter sidewall for that width. |
| R | Radial construction. | It does not indicate the wheel diameter. |
| 16 | Wheel rim diameter in inches. | The tire must fit a wheel of the specified diameter and approved width. |
| 95H | Load index 95 and speed symbol H. | Match or exceed the vehicle maker’s required ratings as applicable. |
In the example, 215 is the tire’s nominal section width, measured in millimetres. It describes the tire’s approximate sidewall-to-sidewall width when mounted under specified conditions; it is not a promise that every brand will measure identically or have the same tread width.
The next number, 65, is the aspect ratio. It expresses sidewall height as a percentage of the section width. For a 215 mm tire, 65% gives a nominal sidewall height of about 140 mm. A lower aspect ratio usually means a shorter sidewall for a given width, but it does not by itself confirm that a tire will fit your vehicle.
R means radial construction. The number after it, 16, is the diameter of the wheel rim the tire is designed to fit, in inches. It is not the tire’s overall outside diameter. That distinction matters when someone refers to a “16-inch tire”: the description alone leaves out width, profile and load and speed ratings.
The characters after the size, such as 95H, are a service description. The number is the load index, a code linked to a tire’s load capacity under specified conditions. The letter is the speed symbol, which identifies a speed category under the applicable tire standards. Neither is a measurement of the tire’s width or diameter.
Use the ratings specified for your vehicle rather than treating a higher-looking number or letter as a complete fitment check. Light-truck tires marked LT may also show load-range information. XL or “Extra Load” indicates a tire designed for higher load capacity at the appropriate pressure; it does not mean it is suitable for every vehicle. Check the vehicle documentation and the tire maker’s specifications if the markings differ from the original fitment.
The tire currently fitted to the vehicle is useful evidence, but it is not the final authority. A previous owner may have installed a non-approved size, and a vehicle may use different sizes on the front and rear axles. Start with the vehicle’s own fitment information, then compare the full tire specification.
Some vehicles are designed for identical tires at all four corners; others leave the factory with different front and rear sizes. Do not assume that one size listed on the sidewall applies to every position. Check the placard and manual, including any information for the spare, before ordering a full set or replacing only one tire.
The sidewall size is important, but it does not contain every detail needed to choose a tire. It does not confirm that a wheel has the correct width or offset, that the tire clears the vehicle, or that a particular seasonal tread is right for your driving conditions. Fitment also depends on the vehicle’s approved specifications and the tire model’s own requirements.
Other sidewall markings can help identify tire features, but they are not part of the size code. For example, M+S is a mud-and-snow marking, while the three-peak mountain snowflake symbol identifies a tire meeting a defined severe-snow performance test. The two markings are not interchangeable. Check the tire’s full specifications if winter performance is part of your decision.
You may also see a maximum pressure or maximum load marking. These are not instructions to inflate the tire to that pressure for everyday driving. Set pressure to the vehicle maker’s recommendation, measured when the tires are cold, unless the vehicle documentation specifies otherwise. Correct pressure supports the intended fitment and helps avoid problems caused by under- or over-inflation.
Sometimes a vehicle maker approves more than one tire size, or a wheel-and-tire change is made as part of a properly checked fitment. But a tire that appears close in diameter is not automatically a safe substitute. A different size can alter clearance, ride, handling, load capacity and speedometer readings. It can also create problems for vehicles whose systems depend on closely matched wheel speeds.
One way to compare nominal outside diameters is to estimate them from the size code. For a 215/65R16 tire, the sidewall height is 215 × 0.65, or about 140 mm. The 16-inch rim is 406.4 mm in diameter, so the estimated overall diameter is about 406.4 + (2 × 140), or 686 mm. This is a calculation from nominal dimensions, not a guarantee of the tire’s actual measured diameter.
Use that estimate only as a comparison tool. Tire models can differ in actual dimensions, and an acceptable diameter alone does not establish that the tire is approved for the wheel or vehicle. If you are considering a non-standard size, ask a qualified tire retailer or vehicle specialist to confirm the complete fitment, including load and speed ratings, wheel compatibility and clearances.
Not without checking the complete approved fitment. Width affects the tire’s relationship to the wheel and vehicle, and a different size may also change clearance and handling. Confirm that the size is approved for your vehicle and wheel before fitting it.
No. The load index is only one part of the specification, and it does not make an otherwise unsuitable tire a correct fit. Match the vehicle maker’s requirements and check the tire type, size and pressure guidance as well.
That depends on the vehicle, the remaining tires and the manufacturer’s guidance. All-wheel-drive vehicles may have particular requirements for matching rolling circumference, so check the manual before replacing only one. A tire retailer can assess the existing tires and confirm a suitable replacement.
It means the tire has radial construction. The wheel diameter is the number immediately after it, such as the “16” in 215/65R16.
Usually, the sidewall pressure marking is a maximum, not the vehicle’s normal target pressure. Use the cold pressure listed on the vehicle placard or in its manual, and follow any vehicle-specific instructions.
To choose a replacement confidently, compare the complete sidewall marking with the vehicle’s approved fitment—not just the wheel diameter. Confirm the size, load and speed ratings, axle position and pressure guidance before ordering. If any part of the specification is unclear, have the proposed tire and wheel combination checked before installation.
