What Do Tire Sizes Mean? How Do Tire Sizes Work? 

Understanding Letters, Numbers and Symbols on the Side of Tires

In this post, we break down what the numbers and letters on the sidewalls of tires mean. Each number, letter and symbol has specific meaning, plus there are key elements that savvy shoppers should know when buying replacement tires for any vehicle. 

On this page, learn tire number meanings, including tire size, load index, speed rating, age and more. In a separate post, we break down how to find out where your tires were made. If you're curious about your wheels, this guide explains how to interpret wheel markings. 

What Do The Numbers on My Tire Mean?

Tire size is shown as a combination of numbers and letters printed on the sidewall. A typical example looks like this: 215/55ZR17 94W

Each part of that code tells you something specific about the tire’s dimensions and construction.

Tire Sizes Explained

Tire Size Numbers

Many people ask, "What do the 3 numbers on a tire mean?" Every tire size includes three numbers that explain width, aspect ration, and rim diameter.

1. Tire Width (215)

The first three-digit number represents the width of passenger tires in millimeters, measured from sidewall to sidewall. In this example, the tire is 215 millimeters wide.

2. Aspect Ratio (55)

The second number is the aspect ratio. This tells you the height of the tire’s sidewall as a percentage of its width. Here, 55 means the sidewall height is 55% of 215 millimeters. A larger aspect ratio means a taller sidewall.

3. Rim Diameter (17)

The last number indicates the wheel diameter in inches. This tire fits a 17-inch wheel.

Other Tire Specs Explained

Tire Construction Letter

Between the aspect ratio and rim diameter, you’ll see a letter. In most cases, this is R, which stands for radial construction. Radial tires are standard on modern passenger vehicles. The tire in this example has a ZR, which means it is a radial tire that has been built for high speed.

Other possible letters include:

• D – Diagonal (bias-ply) construction
• RF – Run-flat tire

For passenger vehicles, R is by far the most common.

Load Index (94)

Next to the tire size, you’ll usually see a number and letter combination, such as:

94W

This tells you two things:

The number indicates how much weight the tire can safely carry. Replacement tires must have the same or higher load index than the manufacturer’s recommendation. We explain tire load index in a separate post. 

Speed Rating (W)

The letter represents the maximum speed the tire can safely sustain under proper conditions. Speed ratings generally increase alphabetically (except for letter H, which comes after U for reasons we explain in a separate post on tire speed ratings). According to the load and speed rating chart, a 94W rating means the tires are approved for 1,477 pounds per tire and 168 mph. 

Week and Year of Production

Every tire includes a DOT code that shows when it was manufactured.

The code begins with “DOT,” followed by a series of letters and numbers. The final four digits indicate the week and year of production.

Example:

DOT CPEX 3ET 0324

• 03 = 3rd week
• 24 = 2024

This tire was manufactured during the 3rd week of 2024.

This post explains how to look up tire manufacturing plants.

Tire Symbols and Markings

Beyond size, load index, and speed rating, tires may include additional symbols and markings.

Three-Peak Mountain Snowflake (3PMSF)

If you see the three-peak mountain snowflake symbol on the sidewall, the tire meets industry standards for severe snow performance. This marking indicates the tire has passed specific snow traction tests.

E-Mark

The E-mark indicates that the tire complies with European Union and international standards related to size, load index, and speed rating. Not all tires sold in the United States carry this marking.

S-Mark

The S-mark confirms that the tire meets EU regulations for road noise limits. Since 2011, new tires sold in the EU must meet these sound standards. Like the E-mark, this symbol is not required for tires sold exclusively in the United States.

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FAQs About How to Read Tire Information

How do you tell what size tires my vehicle needs?

Your vehicle owner's manual will specify your tire size. You can also look on the vehicle specs sticker, which on most vehicles is located on the drivere's side door jamb. This sticker, or placard, explains specifications for your tires, including the recommended air pressure.

What does the P stand for on tires?

P on a tire stands for passenger and means the tire was designed to be used on passenger vehicle types.

What does LT mean on a tire?

LT on a tire stands for light truck and means the tire was designed to be used on light and heavy-duty pick up trucks.

What does ST mean on a tire?

ST on a tire stands for special tire and means that the tires are designed for towing trailers with non-powered axels. 

What does R17 mean on a tire?

R17 on a tire means that the rim size needed would be 17". The "R" actually stands for radial, not rim and is the type of technology the tire uses. 

What does the Z mean in tire size?

The Z means that the tire has been tested over 186 mph

What does the R stand for in tire size?

The R on a tire stands for radial and refers to the type of technology being used within the tire.

What does the first number in a tire size mean?

The first number in a tire refers to the width, measured from shoulder to shoulder in millimeters.

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