How To Read A Tire Size

The letters and numbers molded into a tire sidewall describe the tire's basic specification. Reading them is useful when you are checking the tires already on a vehicle, comparing a possible replacement, or preparing to ask about a wheel-and-tire combination. A size marking can look like a compact code, but each section gives one piece of information about the tire.

That code is only one part of safe tire selection. The vehicle placard, usually found on the driver's door area, and the owner's information are the better starting points for the manufacturer's recommended size, inflation pressure, and load information. Tires that appear similar can differ in dimensions, load capacity, construction, or intended use. When in doubt, confirm the full specification and application before purchase or installation.

Start with a common tire-size example

A common passenger-tire marking looks like P215/60R16 94H. It can be read in sections: P is the service description; 215 is the section width; 60 is the aspect ratio; R identifies radial construction; 16 is the wheel diameter in inches; 94 is the load index; and H is the speed rating. Not every tire uses every prefix or has the same optional markings, but the size, construction, diameter, load index, and speed rating are common elements.

Read the entire sequence from the same tire rather than combining details from memory. The sidewall also carries the brand, model, DOT information, traction and temperature grades, and other markings. Those details can be important, but they do not replace the basic size code.

What the first letter means

In the example, the P stands for P-metric, a passenger-vehicle tire sizing convention. Some tires begin with LT, which commonly identifies a light-truck tire designation. Others have no leading letter, particularly some metric and European-style sizes. The prefix gives context, but it does not mean tires with a similar-looking size are automatically interchangeable.

Passenger and light-truck tires can be designed for different loading and service expectations. Compare the full tire specification, not merely the width and wheel diameter. A vehicle's recommended tire information and the tire's load capacity should remain the reference points when considering a different type of tire.

Understand tire width: the 215

The 215 in P215/60R16 is the nominal section width in millimeters. It describes the tire's approximate width at its widest point when mounted on the specified measuring rim. It is not a promise of the exact tread width or a measurement from one outer sidewall edge to the other under every condition.

Width can vary somewhat with the wheel width, tire design, and manufacturer. A wider number does not automatically make a tire better for a vehicle. It can change clearance, steering feel, road contact, and the way the tire sits on a wheel. If you are comparing sizes, make sure the proposed tire is approved for the wheel width and has appropriate clearance for the vehicle.

Read the aspect ratio: the 60

The 60 is the aspect ratio, sometimes called the profile or series. It means the sidewall height is approximately 60 percent of the section width. With a 215-millimeter-wide tire, the calculated sidewall height is roughly 129 millimeters. It is a proportion, not a measurement in millimeters.

A lower aspect-ratio number generally means a shorter sidewall relative to the tire's width, while a higher number generally means a taller sidewall. Two tires can have the same width and wheel diameter yet have noticeably different overall diameters because of this number. Changing it without checking the full combination can affect vehicle clearance, speedometer readings, and ride characteristics.

Construction letter and wheel diameter

The R in the example means radial construction. Radial tires are common on modern passenger vehicles. Other construction letters exist, but a letter in this position should be read as part of the tire specification rather than treated as an optional style choice.

The 16 means the tire is intended for a 16-inch wheel diameter. This is the diameter at the tire bead seat, not the overall outside diameter of the wheel or tire. A tire marked R16 must be paired with a wheel designed for a 16-inch tire; a 15-inch or 17-inch wheel is not a substitute.

Wheel diameter is only one fitment measurement

Matching the tire's wheel diameter does not confirm that a wheel fits the vehicle. Wheel width, bolt pattern, center bore, offset, brake clearance, and load rating can also matter. A tire size code tells you the wheel diameter the tire needs, not whether a particular wheel will attach to the vehicle. If you are considering a wheel change, verify the wheel's complete fitment separately.

Load index: the 94

The 94 in the example is the load index. It is a code that corresponds to a maximum load capacity for one tire when used at the specified conditions. It is not a direct weight in pounds or kilograms written on the sidewall, so it should be interpreted through a reliable load-index chart or the tire manufacturer's information.

The required load capacity depends on the vehicle and its recommended tire specification. Do not assume a tire is suitable simply because it has the correct width, profile, and diameter. A replacement should meet the vehicle manufacturer's requirements for load capacity. If the vehicle has different front and rear sizes, follow the vehicle-specific guidance rather than trying to match all four tires by appearance.

Speed rating: the H

The H after the load index is the speed rating. It identifies a tire's tested high-speed capability under defined conditions; it is not a recommendation to drive at that speed and does not override posted limits, weather, traffic, tire condition, or safe-driving judgment. Speed ratings use letters, and their order is not always intuitive, so compare the actual rating rather than assuming that a later-looking letter has a particular meaning.

Maintain the speed rating required or recommended for the vehicle unless a qualified tire professional or the vehicle manufacturer provides appropriate guidance. Mixing tire types or ratings can affect how a vehicle responds. When replacing fewer than four tires, ask how the new tire's size, construction, load index, and speed rating relate to the tires that remain on the vehicle.

Other sidewall markings worth recognizing

Many tires include M+S or a three-peak mountain snowflake symbol. These markings refer to different categories of winter-related performance and should not be treated as interchangeable. A tire may also show XL for extra load, which relates to its load capability when used as specified. The word Tubeless is common on modern tires, while directional arrows or an Outside marking indicate how a tire must be mounted.

The DOT code identifies the tire's production information. Its final four digits commonly show the week and year of manufacture, such as 1425 for the fourteenth week of 2025. Age alone does not tell you a tire's current condition, but it is useful context alongside inspection for damage, cracking, tread condition, repairs, and storage history. A qualified tire professional can help evaluate concerns that are not clear from a visual check.

Find the vehicle's recommended size

The size on the tire currently installed may not be the size originally specified for the vehicle. Previous owners may have changed wheels or tires, and a spare can be different from the regular tires. Check the vehicle's tire-information placard, owner's material, or manufacturer guidance before assuming the existing marking is the correct target.

The placard can also list front and rear tire sizes separately, recommended cold inflation pressures, and vehicle loading information. Do not use the maximum pressure molded onto the tire sidewall as the vehicle's routine inflation recommendation. The correct cold pressure is vehicle-specific and should be checked with a dependable gauge when the tires have not been driven enough to warm up.

Compare a replacement tire carefully

When comparing a replacement, write the full sidewall code down in order. Then compare the size, construction, wheel diameter, load index, speed rating, and any relevant special markings. Check whether the tire is intended for the same axle position and whether it has a directional or asymmetric tread design. If the vehicle uses a staggered setup, all tires may not share the same specification.

For a used tire, the visible size marking is only the beginning. Ask about the tire's condition and inspect it appropriately before making a decision. The site publishes used tires and wheels as a parts category, but current inventory and suitability must be confirmed directly. For questions about installation or related work, review the published tire work information and ask about current service availability.

FAQ: reading tire sidewall numbers

What does 225/65R17 mean on a tire?

It describes a tire with a nominal 225-millimeter section width, a sidewall height that is approximately 65 percent of that width, radial construction, and a 17-inch wheel diameter. Check the remaining sidewall markings for its load index and speed rating.

Can I use a different tire size if it fits the wheel?

Wheel diameter alone is not enough. A different size can change overall diameter, clearance, load capacity, and vehicle behavior. Compare the vehicle's recommendations and obtain fitment guidance before changing size.

Is the number on the tire the same as the recommended size?

Not necessarily. The tire on the vehicle may have been replaced with a different size. Use the vehicle placard or manufacturer information to identify the recommended specification.

What information should I share when asking about a tire?

Share the full sidewall code, vehicle year, make, model, and whether the tire is for the front or rear. You can confirm tire availability and fitment details directly with A & D Auto Parts & Repair.