A tire’s sidewall contains more than a brand name: its markings show the tire’s size, construction, load capacity, and speed rating. Learning how to read tire size helps drivers check whether a tire matches their vehicle, compare replacement options, and recognize when a tire may not meet the vehicle’s requirements. A common marking, such as P215/65R16 95H, becomes easier to understand when each letter and number is read in order.
Where to Find Tire Size Information
The tire size is printed on the sidewall, usually near the tire’s brand and model name. It is a sequence of letters and numbers, often followed by a load index and speed rating. The exact layout can vary by tire type and manufacturer, but the main size elements appear in a consistent order.
Drivers should also check the vehicle’s recommended tire size. It is commonly listed on a placard inside the driver’s doorjamb, on the fuel-filler door, or in the owner’s manual. The vehicle placard typically specifies the original tire size, recommended cold tire pressure, and load information. Those vehicle specifications—not the tire’s maximum pressure printed on its sidewall—should guide routine inflation and replacement decisions.
How to Read a Tire Size Example
Consider the marking P215/65R16 95H. It can be read as a passenger-car tire with a 215-millimeter section width, an aspect ratio of 65, radial construction, and a tire designed to fit a 16-inch wheel. The additional 95H identifies the tire’s load index and speed rating.
| Marking | What It Means |
|---|---|
| P | Passenger-type tire designation |
| 215 | Nominal section width in millimeters |
| 65 | Aspect ratio: sidewall height as a percentage of width |
| R | Radial tire construction |
| 16 | Wheel diameter in inches |
| 95 | Load index, which corresponds to a specified load capacity |
| H | Speed rating under defined test conditions |
Spaces or punctuation between the size and service description can differ. Some sidewalls show the service description in parentheses, and some tire types use additional letters or numbers. The characters should be interpreted together rather than treated as one measurement.
What the Tire Size Numbers Mean
Tire Type: The First Letter
The first letter, when present, indicates the tire’s general type or intended application. P stands for a P-metric passenger tire, commonly used on cars, minivans, and some SUVs. LT identifies a light-truck tire designed for certain trucks, vans, and heavier-duty applications. ST means special trailer tire, intended for trailer use rather than passenger vehicles.
A marking without a leading letter may follow a European metric sizing convention. A tire’s intended use should be confirmed from its full sidewall markings and manufacturer information. A tire that physically fits a wheel is not necessarily appropriate for a particular vehicle; load capacity, vehicle requirements, and tire type matter too.
Section Width
In a size such as 215/65R16, 215 is the nominal section width in millimeters. It describes the approximate width from sidewall to sidewall when the tire is mounted on a specified measuring rim and inflated under prescribed conditions. It is not a promise that every tire with that number will measure exactly 215 millimeters in service. Actual dimensions can vary by model, rim width, and measurement method.
To convert millimeters to inches, divide by 25.4. A nominal width of 215 millimeters is about 8.5 inches. This conversion is useful for comparisons, but the tire’s labeled metric size remains the standard reference.
Aspect Ratio
The number after the slash is the aspect ratio, expressed as a percentage. In 215/65R16, the sidewall height is nominally 65% of the tire’s section width. That makes the estimated sidewall height 215 × 0.65, or about 140 millimeters.
A lower aspect ratio generally means a shorter sidewall relative to the tire’s width; a higher ratio means a taller one. Aspect ratio affects tire dimensions and can influence ride and handling characteristics, but it does not by itself determine whether a tire will fit. Overall diameter, wheel clearance, vehicle specifications, and the tire manufacturer’s fitment information also matter.
Construction and Wheel Diameter
The letter R means radial construction, the most common design for modern passenger tires. Radial describes how the tire’s internal body cords are arranged. It does not mean “rim” or “radius.” Less commonly, a sidewall may show D for diagonal or bias-ply construction.
The number after the construction letter is the wheel diameter in inches. A 16-inch tire in the example is made for a 16-inch-diameter wheel. It will not properly fit a 15-inch or 17-inch wheel. This measurement refers to the wheel, not the tire’s overall outside diameter.
Load Index and Speed Rating
After the main size, the service description typically includes a load index and speed rating. In 95H, 95 is the load index and H is the speed symbol. The load index is a code that corresponds to a maximum load per tire under specified conditions; it is not the load amount in pounds. For example, load index 95 corresponds to 1,521 pounds per tire in the standard load-index table.
The speed rating indicates a tire’s capability to operate at a specified speed under controlled test conditions when properly inflated and carrying an appropriate load. It is not a recommended driving speed or a guarantee of performance in every situation. Speed symbols range from letters such as L, T, H, and V to higher-rated symbols. The corresponding rating should be checked against the vehicle maker’s requirements and the tire manufacturer’s specifications.
Replacement tires should meet or exceed the vehicle’s required load capacity and should have an appropriate speed rating. A higher rating alone does not make a tire a suitable replacement. Drivers should verify the complete specification, including size, service description, and any vehicle-specific requirements.
Common Tire Size Variations
Metric and P-Metric Sizes
Many passenger tires use a P-metric size beginning with P, while other passenger tires use metric sizing without that initial letter. Similar-looking sizes can have differences in load capacity or application. When comparing tires, drivers should not assume that matching width, aspect ratio, and wheel diameter makes two tires identical in every important respect.
Light-Truck Sizes
Light-truck tires can use metric-style sizing with an LT prefix, such as LT245/75R16, or flotation sizing such as 33×12.50R17. In the flotation example, 33 is the approximate overall tire diameter in inches, 12.50 is the approximate section width in inches, and 17 is the wheel diameter in inches. These values are nominal; actual dimensions vary by tire model and measuring conditions.
LT tires may have load ranges such as C, D, or E, which relate to a tire’s construction and load capability at specified inflation pressures. Load range is not the same as load index. The correct pressure and capacity depend on the tire, vehicle, and load, so drivers should consult the vehicle manufacturer and tire documentation rather than inflate to the sidewall maximum by default.
Run-Flat and Other Markings
Run-flat capability is identified with manufacturer-specific terms or symbols, which may include markings such as RFT, ROF, or ZP. The exact designation depends on the brand. Run-flat tires have limitations, including restrictions on how far and how fast the vehicle can travel after pressure loss. The vehicle manual and tire maker’s instructions provide the relevant limits.
Other sidewall information may include a maximum load, maximum inflation pressure, traction and temperature grades, or a three-peak mountain snowflake symbol. These details are useful, but they are not substitutes for the tire-size and vehicle-fitment checks. A tire’s maximum pressure marking is not the normal inflation target for everyday driving.
Tire Size Is Not the Same as Overall Tire Diameter
The numbers in a common metric tire size do not directly state the tire’s total height. Approximate overall diameter can be calculated from the sidewall height and wheel diameter. For a 215/65R16 tire, the sidewall is about 140 millimeters, or 5.5 inches. Two sidewalls plus a 16-inch wheel produce an estimated overall diameter of about 27 inches.
This calculation is only an estimate. Tire model, tread depth, rim width, pressure, and measurement conditions affect actual dimensions. Drivers considering a different size should confirm fitment with a qualified tire professional or the vehicle and tire manufacturers. A change in overall diameter can affect speedometer readings, ground clearance, gearing, braking systems, and clearance around suspension or body components.
How to Choose a Replacement Tire Size
- Check the vehicle placard and owner’s manual. These identify the manufacturer’s recommended size and pressure for the vehicle’s original configuration.
- Match the full specification. Compare tire type, width, aspect ratio, construction, wheel diameter, load index, and speed rating—not just the first group of numbers.
- Confirm wheel compatibility. The tire’s wheel diameter must match the wheel, and the wheel width must be approved for that tire.
- Verify any approved alternatives. Some vehicles have different factory-approved sizes for different trims or wheel packages. Use the information for the specific vehicle.
- Ask a qualified tire professional before changing size. An alternative size needs checks for load capacity, clearance, wheel fit, and vehicle-system effects.
When replacing only one or two tires, the vehicle manufacturer may specify how the new tires should be matched to the existing set. Differences in size, tread depth, or type can affect handling and, on some vehicles with all-wheel drive, drivetrain operation. The owner’s manual or a tire professional can help determine the appropriate replacement plan.
Sidewall Information That Is Not the Tire Size
The DOT Tire Identification Number is separate from the size marking. It identifies information related to the tire’s manufacture and includes a date code at the end. On newer tires, the last four digits indicate the week and year of manufacture: for example, 3523 means the 35th week of 2023. This date code does not identify the tire’s size or guarantee its remaining service life.
Treadwear, traction, and temperature grades are also separate from the size. These Uniform Tire Quality Grading marks provide comparative information under specified test conditions, but they do not describe every aspect of tire performance. For detailed explanations of tire safety and labeling, drivers can consult the National Highway Traffic Safety Administration’s tire safety resources.
Quick Tire Size Reading Checklist
- Read from left to right: identify the tire type, width, aspect ratio, construction, and wheel diameter.
- Read the service description: note the load index and speed rating after the size.
- Check the vehicle placard: use its recommended size and cold inflation pressure as the starting point.
- Do not confuse pressure markings: the tire’s maximum pressure is not automatically the vehicle’s recommended pressure.
- Confirm before changing sizes: verify capacity, wheel fit, clearance, and vehicle compatibility.
Once the sequence is familiar, a tire size such as P215/65R16 95H provides a useful snapshot of the tire’s basic dimensions and service category. The safest replacement choice is one that matches the vehicle’s specifications and is approved for its wheels, load, and intended use.