Tire Size Calculator

Enter your stock tire size :
/ - R
Enter the new tire size :
/ - R
Please enter a speedometer reading: MPH or KM/H


Stock tire width is inches. New tire width is inches.
Stock tire thickness is inches. New tire thickness is inches.
Stock tire diameter is inches. New tire diameter is inches.
When your speedometer indicates MPH / KM/H, you would actually be travelling MPH or KM/H.

When you are supposed to make a decision, it is always preferable to take measurements beforehand. Not only does this provide you with a rough idea of all of the required information, but also yields room for comparison.

Similarly, when you are planning to buy tires, you need to be able to calculate and compare their sizes. Hence, in such situations, online tire calculators are a great source of help. These tire size conversion calculators allow you to enter tire dimensions in order to calculate the size.

However, before starting right off, you must be well-informed about certain aspects regarding the tire size calculator. For instance,

  • how tire dimensions work?
  • what is the format of writing tire dimensions?
  • how to calculate tire size with the given dimensions?

These questions are just the basic ones while many other small details form an integral part of tire size calculation. Therefore, we have formulated this guide for your ease.

This comprehensive guide on Calculator for tire size will be all you need to calculate and compare tire sizes!

We also formulated a guide on Anti-Spin Differential Rear Axles. You can find out all about them in the article Everything You Need to Know About Anti-Spin Differential Rear Axles.

1. Tire Size Calculators

Calculators for measuring tire sizes are a great tool for comparing tire measurements. These tire size conversion calculators usually allow you to enter the dimensions of the tire without taking in any other factors liking the company or the type. However, it is equally necessary to consider the physical limiting factors. For instance, a 285 75R20 type tire cannot fit a car made for a 185/80 R13 tire. To avoid such circumstances, this guide is your ultimate source.

Some of the most easily available and comprehensive calculators that are available on the internet are:

  • Tire Size Calculator on Oponeo.co.uk
  • 1010 Tire Calculator on 1010tires.com
  • Tiresize.com

2. Dimensions for Tire Size

When you wish to calculate the size of the tire, you must take some measurements. These measurements are dimensions required by any calculator, that you are likely to find online. Once you enter these dimensions in their right fields, the tire size conversion calculator will do the calculations by itself and provide you with the answer.

It must be noted here that, at many times, the dimensions of the tire are not so easy to determine. The way the dimensions are mentioned is not so common and someone with not much experience will surely feel some level of difficulty. Moreover, the most basic dimensions of a tire are its diameter and width, but there can be many other important factors to consider, too.

Tires usually come with a certain combination of letters and numbers as their identifiers. These combinations are used to set apart different types and dimensions of the tires. Therefore, whenever, we are trying to figure out the different tire dimensions, we must always look for these combinations. Hence, this guide will come in handy in such situations.

Following are some of the other tire size dimensions that you must consider for calculating tire sizes. For the scope of better understanding, we will be considering a tire with the identifier marked as P215/65 R15 91S


  • Tire Type

On some tires, the presence of the first one or two letters indicates the type of tire. For instance, in the United States, some cars state P, which indicates it is a tire for passenger vehicles. These P-metric tires also hold certain standards in the US for reference. On the other hand, Euro-metric tires have no letters on them. Moreover, tires with the letters LT are made for light trucks, that can withstand higher pressures than the passenger-vehicle tires.

  • Tire Width

In tire measurements, tire width is an important factor. The width of the tire is mentioned at the very start of the identifier. For the example provided above, the tire width is the number right after the first letter, corresponding to the first 3 digits. This means that the width is 215 and is measured in millimeters.

It is to be noted that the tire width is measured from one sidewall of the tire to the other.

  • Aspect Ratio

The next numbers after the slash represent the aspect ratio of the tires. Aspect Ratio basically indicates the ratio of the tire cross-section’s height to the width. For the example provided, this would mean that the tire’s height is 65% of the width of the tire. The aspect ratio is directly proportional to the sidewalk of the tire. This specifies that a bigger aspect ratio means a bigger sidewalk and vice versa.

  • Construction

There can be two different construction types of tires, based on the way they are manufactured internally. The next letter in the identifier shows just that. In the example used for this guide, the letter R refers to the construction type Radial. The other construction type is Cross-Ply.

  • Wheel Diameter

For tire size calculators, it is necessary to know the wheel diameter. The diameter of the wheel is important to determine since it shows which kind of tire will fit the wheel. The wheel’s diameter is measured from one side to the other. In the example given above, the number next to the construction type, which is 15, refers to the wheel’s diameter. However, it is to be noted that the wheel diameter is given in inches and not in millimeters.

  • Load Index

After the wheel’s diameter, the next two numbers indicate the load index of the tire. The load index means that the maximum load that the tire can bear after being completely inflated. The sidewalk also has the same information and in both pounds and kilos.

  • Speed Rating

The letter at the very end is meant to indicate the speed ratings of the tire. These ratings are provided by the manufacturers that the speed of the vehicle must not be exceeded while using a particular type of tire.

For more on Jeep tires, you can go through our article on Jeep JK 33 inch Tires Stock Wheels- How-To Guide.

This alphanumeric combination is mostly present on the tire itself and on some other parts of the vehicle. For instance, the information can be found inside the door of the glove box, the door jamb on the driver’s side and, within the hatch of the gas tank.

Besides the above-given factors, there is other information sometimes available, as well. Some other information may include:

  • DOT Symbol:

These letters on the tire’s side show that the tire is in compliance with the Federal Motor Vehicle’s safety standards.

  • Tire Identification Number:

The Tire Identification number follows the DOT Symbol and is a combination of 12 alphabets and numbers that indicate where and when that particular tire was manufactured.

  • UTQG

The Uniform Tire Quality Grading is a rating system introduced by the Department of Transportation US. Firstly it includes traction grading, referring to how the tire performs in wet weather conditions. Secondly, it shows how the tire performs in high temperatures as well as its ability to withstand heat. Lastly, the treadwear grade tells the users how long the tire can last, based on their performance in government-standardized tests.

3. Tire Size Comparison

Most drivers are well-known for the idea of changing the tires of their vehicles after a certain time. Not only that, but the drivers also give grave importance to the fact that after proper tire size comparison and compatibility, the tires should be changed. Therefore, with this guide’s help, we would aid you in making the right comparisons.

We have comprised a list of some checks that you should establish when you need to compare tires for your vehicle.

Some tire calculators also come with tire comparison charts that can be of great help in comparing different sizes.

When should the tires be changed?

In the most basic sense, a change is only applicable when the older tire is not much of use. However, some drivers also tend to change the tires to improve the performance of the vehicle. Changing tires can help better some parameters which ultimately result in a better driving experience.

On the other hand, there can be some drawbacks to changing the tires, too. In some cases. tire-size equivalents are better an option than making tire size interchanges entirely. Therefore, it is highly recommended to compare the pros and cons of tires before making the final decision.

What is the acceptable tire size?

It is necessary to know the difference in the outer diameter when using a tire size comparison tool.  Many tools are present on the internet that can calculate it for you. Mostly it is represented in percentages and some calculators even mention the acceptable percentages for the tire to fit accurately.

If you wish to know more about your Wrangler Radio, do check our guide on Everything You Need to Know About Jeep Wrangler Factory Radio Specs.


Tire size calculators are easily available on the internet. All you need to do is to take some tire measurements such as tire circumference or width and enter those into the respective fields. The results can provide you with tire size in inches or millimeters, whatever you need. Moreover, you can also find

  • width calculators
  • tore diameter calculator
  • tire conversion calculator
  • rim size calculator
  • tire size visualizer

However, using these can become a little tricky if you are unaware of tire measurements and dimensions. This guide, therefore, sums it all up for you!