How to read a tire size

In P225/65R17 95H, 225 is the width in millimeters, 65 is the sidewall height as a percentage of that width, R means radial construction, 17 is the wheel diameter in inches, 95 is the load index and H is the speed symbol. The leading P identifies a passenger tire. The vehicle’s original tire size and inflation information are printed on its driver-side door-jamb placard.

The sidewall tells you what tire you have; the placard tells you the size selected for your vehicle. Read both before replacing tires. A size comparison can help you understand dimensional changes, but it cannot confirm fitment.

The first number, 225, is nominal section width in millimeters, measured across the tire from sidewall to sidewall on its specified measuring rim. Actual dimensions vary somewhat by model and rim width.

The number after the slash, 65, is aspect ratio: the sidewall height is 65 percent of the section width. Here, one sidewall is 225 × 0.65 = 146.25 mm, or about 5.76 inches.

R means radial construction, the standard construction for modern passenger tires. The final number, 17, is the diameter of the wheel rim in inches; it is not the tire’s overall diameter.

After the size, 95H is the service description. 95 is a load index that corresponds to a rated load under specified conditions; H is the speed symbol. Consult the tire maker’s load and speed information for the actual ratings. See load index and speed rating for more detail.

The prefix describes a tire category: P is P-metric passenger, LT is light truck, ST is special trailer, and T marks a temporary spare. A prefix matters because tire standards and load use can differ; matching the numbers alone is not enough. Do not substitute a trailer tire for a vehicle tire.

Some truck tires use flotation notation such as 33x12.50R15. The first number is approximate overall diameter in inches, the second is nominal width in inches, R indicates radial construction, and 15 is the rim diameter. In this example, the nominal sidewall height is (33 − 15) ÷ 2 = 9 inches. See how flotation tire sizes work.

For metric notation, calculate overall diameter as wheel diameter plus two sidewalls. For 225/65R17, 225 × 0.65 = 146.25 mm per sidewall. Convert both sides to inches: 2 × 146.25 ÷ 25.4 = 11.52 inches. Add the 17-inch rim: 17 + 11.52 = 28.52 inches overall (rounded to two decimals). This is a calculated nominal dimension; real measured diameter can vary.

Look for the letters DOT followed by the tire identification number (TIN) molded into the sidewall. Under 49 CFR 574.5, the full TIN includes plant and tire identification information and ends with a four-digit date code for tires made since 2000. The first two digits are the week of manufacture and the last two are the year: 2324 means the 23rd week of 2024.

The complete TIN may appear on only one sidewall, so the date code can face inward. A date identifies manufacture, not the tire’s condition or a universal replacement deadline. Inspect tires regularly and follow the vehicle and tire maker’s guidance.

The first part of the TIN identifies the manufacturing plant, followed by a code assigned by the tire maker to identify the tire’s size and other characteristics. The exact placement and format of the letters and digits can vary, but the DOT marking identifies the sequence as a Department of Transportation tire identification number. If the visible side only has a partial sequence, check the opposite sidewall for the complete code.

Use the date as one piece of maintenance information alongside tread depth, damage, storage history and inspection. Tires can age while a vehicle is parked, and a code by itself cannot tell you whether the rubber is safe. A tire professional can inspect cracking, bulges, punctures and other conditions that are not captured by the date digits.

Find the tire and loading information label, usually on the driver-side door jamb or door edge. It lists the vehicle manufacturer’s original tire size and recommended cold inflation pressure, along with loading information. Some vehicles have additional placard information in the owner’s manual.

The placard is specific to the vehicle as built, so use the label on your own vehicle rather than relying on a label shown online for a similar model. Read the front and rear tire entries if they differ, and note whether the spare has a separate size or pressure. Tire pressure on the placard is the recommended cold pressure; the maximum pressure molded into a tire is a different figure and is not a replacement recommendation.

If the label is missing or unreadable, the owner’s manual or the vehicle manufacturer can help identify the original specification. Do not infer a safe pressure from the tire’s sidewall maximum. Recheck pressure when tires are cold and follow the instructions in the manual, especially when the vehicle is carrying a heavy load.

Use the placard as the starting point when replacing tires, and check the owner’s manual for any alternate approved sizes. Federal standard 49 CFR 571.110 includes requirements for tire selection and vehicle tire information labels. Aftermarket wheels, modifications, or a different tire size call for a fitment check by a qualified professional.

If you are considering a diameter change, compare the effect with the speedometer guide and try the tire size calculator.