How to Read Tire Size

The string of numbers and letters stamped on your tire sidewall looks like a secret code, but it tells you almost everything you need to know about the rubber under your car. Reading tire size correctly helps you buy the right replacements, keep your speedometer accurate, and stay safe on the road. In this guide we break down a typical code such as P215/65R16 95H piece by piece, then show you exactly where to find the size that fits your vehicle and why matching it matters.

Decoding a Sidewall Code Like P215/65R16 95H

Every modern passenger tire carries a standardized size code on its sidewall. Using P215/65R16 95H as our example, each part of that string describes a specific physical characteristic of the tire. Once you know what each segment means, you can read any tire size at a glance and compare options with confidence.

The full code breaks into seven parts: the type letter (P), the section width in millimeters (215), the aspect ratio (65), the construction letter (R for radial), the wheel diameter in inches (16), the load index (95), and the speed rating (H). The next sections walk through each of these so you understand not just what the numbers say, but why they matter when you shop for new tires.

The Type Letter and Section Width

The first character is the type letter. A leading P stands for P-metric, meaning the tire is designed for passenger vehicles built to North American standards. You may also see LT for light truck, ST for special trailer, or no letter at all, which usually indicates a Euro-metric tire. The type letter affects how the tire’s load capacity is calculated, so it is worth noting before anything else.

The three-digit number that follows, 215 in our example, is the section width measured in millimeters. This is the width of the tire from one sidewall to the other at its widest point when properly inflated and mounted. A larger number means a wider tire, which generally puts more rubber on the road. Section width must match what your vehicle and wheels are built for, so it is one of the most important figures to get right.

Aspect Ratio, Radial Construction, and Wheel Diameter

After the slash comes the aspect ratio, 65 in our example. This two-digit number is the height of the sidewall expressed as a percentage of the section width. An aspect ratio of 65 means the sidewall height equals 65 percent of the 215 millimeter width. A lower number gives a shorter, stiffer sidewall and a sportier feel, while a higher number gives a taller sidewall and a softer, more cushioned ride.

The letter R that follows stands for radial construction, which describes how the internal body plies are arranged. Nearly all passenger tires sold today are radials, so you will see R on the vast majority of codes. The final number in this group, 16, is the wheel diameter in inches. It tells you the size of the rim the tire is built to fit, so a 16 must go on a 16 inch wheel and nothing else.

The Load Index and Speed Rating

The number near the end of the code, 95 in our example, is the load index. It is a coded value that corresponds to the maximum weight each tire can safely carry when inflated to its rated pressure. A load index of 95 translates to roughly 1,521 pounds per tire on a standard chart. Higher numbers carry more weight, and you should never fit a tire with a lower load index than your vehicle requires.

The final letter, H in our example, is the speed rating. It indicates the maximum sustained speed the tire is engineered to handle. H corresponds to about 130 miles per hour, while ratings such as V, W, and Y are rated for even higher speeds. The speed rating also reflects general performance characteristics, so matching or exceeding your vehicle’s original rating keeps handling and safety where the manufacturer intended.

Where to Find Your Size and Why Matching It Matters

There are two reliable places to find the correct tire size for your car. The first is the sidewall of your current tires, where the full code is molded into the rubber. The second, and often more authoritative source, is the placard on the driver’s side door jamb. This sticker lists the original size specified by the manufacturer along with the recommended inflation pressures, and it reflects what the vehicle was engineered to use even if someone fitted different tires later.

Matching the correct size matters for more than just fit. The wrong section width or diameter can rub against suspension components, throw off your speedometer reading, and change how the car handles and brakes. An undersized load index or speed rating can lead to overheating or failure under load. When you are ready to shop, comparing options that match your placard is the safest path, and a roundup of the best tires for cars is a useful place to start narrowing your choices.

Frequently Asked Questions

What does the R in a tire size mean?

The R stands for radial construction, which describes how the internal plies of the tire are arranged. Radial tires have body plies that run across the tire at a 90 degree angle to the direction of travel. Almost every passenger car tire sold today is a radial, so you will see R in the vast majority of size codes.

Should I match the speed rating on my original tires?

Yes, you should match or exceed the speed rating that came with your vehicle. The speed rating reflects how much heat and stress the tire can handle, and it also signals general handling characteristics. Choosing a lower rating than the original can reduce safety margins, so it is best to stay at the manufacturer’s rating or higher.

Is the door jamb placard more reliable than the sidewall?

The door jamb placard is usually the most authoritative source because it lists the size the manufacturer originally specified for your vehicle. The sidewall shows the size of the tire currently fitted, which may differ if a previous owner changed it. When in doubt, follow the placard for size and inflation pressure.

The Bottom Line

Reading a tire size is simple once you know that each part of a code like P215/65R16 95H stands for a specific measurement: the type letter, the section width in millimeters, the aspect ratio, R for radial, the wheel diameter in inches, the load index, and the speed rating. Check your sidewall and the driver’s door jamb placard to confirm the size your vehicle needs, and always match those specifications when you buy. Getting the size right protects your safety, keeps your speedometer honest, and ensures your new tires perform exactly as the engineers intended.