How Do You Measure Tire Size?

How Do You Measure Tire Size

Unfortunately, tires aren’t one-size-fits-all. All you have to do is walk into your local auto shop or a Goodyear to see how many different sizes there are. 

To get the right one, you’re probably inquiring, “How do you measure tire size?” It might sound like an easy question, but if you don’t do it every day, you’ll have no idea where to start. 

That’s where our guide comes in! Read on to learn everything you need to know about “How do you measure tire size?”

What You Need to Measure Tire Size 

Though we’re talking measurements, you won’t need a ruler, tape measure, or anything of the sort. 

Car manufacturers recommend sizes for their vehicles. All you have to do is find the size, understand what it means, and purchase the corresponding model. 

Not sure where to find the size? Check your current tire. There should be a string of numbers and letters running across the rubber. 

If you don’t think your current tire is the correct size, check the owner’s manual. The manufacturer should also list the recommended size on the placard inside of the driver’s door. 

How to Read Tire Size 

how are tire sizes measured

Once you find the string of numbers and letters, you can provide this information to an auto shop. A professional will match you with the correct model. 

However, you might want to know what all of the numbers and letters mean. This information can be empowering and help you shop on your own. 

Below, we clear up the confusion by breaking down what all of the letters and numbers mean. 

Measurement Standards 

Before diving in, we should note that manufacturers adhere to different measurement standards. Tires can be P-metric, LT-metric, Euro-metric, C-type, etc. 

The various measurement standards can seem confusing, but don’t worry. The numbers and letters stay pretty much the same. For instance, consider these two models: 

  • P225/70R16 97H
  • 225/70R16 98H

The first one is P-metric (as the “P” at the beginning indicates), and the second is Euro-metric. However, as we discuss below, all of the other numbers and letters represent the same measurements.


For the rest of our guide, we’ll be using P225/70R16 97H as our example. 

The first three numbers indicate the width of the tire in millimeters. In this case, the width is 225 mm.

Aspect Ratio 

To find the aspect ratio, look at the first two numbers after the first forward slash. Our example has an aspect ratio of 70, meaning the height is equal to 70% of the tire’s width. 

how do you measure a tire


Following the aspect ratio, you’ll find a letter for the construction rating. Most manufacturers recommend a construction rating of “R,” which stands for radial. You may also see a “D” (diagonal) or “B” (bias ply).

Rim Diameter

There should be a two-digit number following the construction rating to indicate rim diameter. In our example, the rim diameter is 16. This number is always listed in inches. 

Load Index

The next number (97) tells us the load index. If you get a tire that has a load index lower than what the manufacturer recommended, it may not be able to support the weight of the vehicle. 

 how do you measure tire size

Speed Rating

The final letter is the speed rating. As you might’ve guessed, this rating refers to the rubber’s maximum speed capabilities. In our case, the “H” indicates a maximum speed of 130 miles per hour (or 210 kilometers per hour). 

Additional Information

Note that some models may have additional information. For instance, consider this example: LT245/75R17 119/116R Load Range E. You’ll see that it lists two load indexes instead of one (119 and 116). There’s also a load range classification. 

When You Should Measure Tire Size 

Whether you need to replace your tire because it’s flat or for aesthetic reasons, you need to make sure you get the right size. 

Having the right size will ensure your tire lasts as long as it should. Additionally, it will protect your vehicle and keep you safe on the road. 

Looking at the numbers and letters on the rubber is one of the easiest ways to determine size. However, if you want to make sure this size is what the manufacturer recommends, consult your owner’s manual or the placard on the inside of the driver’s door. 

The Bottom Line 

As we’ve demonstrated, the answer to “How do you measure tire size?” isn’t as complicated as you might’ve thought. All you have to do is check the manufacturer’s recommendation and buy the appropriate model. If you want to know what all of the numbers and letters mean, simply refer back to this guide!

If you find our blog helpful, feel free to check out:

How To Measure Tire Rim Size
How To Read Trailer Tire Sizes
How To Convert Tire Size To Inches
How To Find Out Tire Size
How To Find Tire Diameter