How Do You Tell a Tire Size - Complete Guide to Reading Tire Sizes

When it comes to vehicles, one of the most common questions is: how do you tell a tire size? Knowing how do you tell a tire size is essential for safety, performance, and ensuring you purchase the correct replacement tires. In this article, we will explore how do you tell a tire size, what the numbers mean, and why it matters.

Understanding Tire Size Markings

The sidewall of every tire contains a series of numbers and letters. But how do you tell a tire size from these markings? For example, a typical tire might read: 205/55R16 91V. Each part of this code provides information about the tire's width, aspect ratio, construction, and diameter. Learning how do you tell a tire size from these numbers can help you make informed decisions when buying new tires.

Why Knowing Tire Size Matters

If you don't know how do you tell a tire size, you risk purchasing the wrong tires for your vehicle, which can affect handling and safety. Always check your owner's manual or the placard on your car door to confirm the correct size. For a quick check, try our tire calculator to compare or calculate tire sizes instantly.

Detailed Guide to Tire Size Markings

Metric Sizing Explained

Most passenger cars, SUVs, and light pickups use either P-Metric or Euro-Metric tires. If you see a "P" before the number sequence (e.g., P225/70R16 97H), it indicates a P-Metric tire, standardized for passenger vehicles in North America. Euro-Metric tires, commonly found in Europe, have no preceding letter (e.g., 225/70R16 98H). Both types are designed for passenger vehicles, including cars, minivans, SUVs, and light-duty pickups.

For heavier vehicles like 3/4 ton and larger trucks or vans, you may encounter LT-Metric (e.g., LT245/75R17 119/116R) or Euro-Metric Commercial (C-Type, e.g., 225/65R16C 121/119R) tires. LT-Metric tires are built for light trucks and will have "LT" before the size, while C-Type tires have a "C" after the rim size. Temporary spares start with "T" (e.g., T125/90D16), and special trailer tires begin with "ST" (e.g., ST205/75R15).

Key Tire Size Elements

• Width: The first number (e.g., 225 in P225/70R16) indicates the tire's width in millimeters, measured from sidewall to sidewall.
• Aspect Ratio: The number after the slash (e.g., 70 in P225/70R16) is the aspect ratio, representing the height of the sidewall as a percentage of the width.
• Construction: The letter after the aspect ratio shows the internal construction—"R" for radial (most common), "D" or "B" for bias ply, "RF" for run-flat, and "ZR" for high-speed tires.
• Rim Diameter: The next number (e.g., 16 in P225/70R16) is the rim diameter in inches.
• Load Index: The number following the rim size (e.g., 91 in P225/70R16 91S) tells how much weight the tire can support. Passenger tires usually have one load index; light truck and commercial tires may have two (for single/dual applications). "XL" indicates Extra Load, and Load Range (e.g., Load Range E) is often seen on truck tires.
• Speed Rating: The final letter (e.g., S in P225/70R16 91S) indicates the maximum speed capability of the tire. Always match or exceed your vehicle’s original speed rating when replacing tires.

Flotation Sizing (for Off-Road & Light Truck Tires)

Some off-road and light truck tires use Flotation sizing (e.g., 31x10.50R15LT):

• Overall Diameter: First number is the overall diameter in inches.
• Section Width: Second number is the section width in inches.

Tips for Reading Tire Sizes

• Always check your vehicle’s placard or owner’s manual for the correct tire size.
• Remember, similar load index numbers in P-Metric and Euro-Metric systems may represent different actual load capacities.
• Replacement tires should have the same or higher speed rating and load index as the originals.

For more on tire size calculator, rim width compatibility, or to convert units like psi to bar, explore our other guides and calculators! You can also calculate tire size for any vehicle model with our free tool.

Published: August 17, 2025