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Tire Size Calculator and Tire Size Comparison Calculator
Andrew Cilio
/ Feb 23 2023
Choosing the right tire size increases safety, improves handling, and relieves stress on brake components. So if you're shopping for new tires, our tire size calculator can show you any tire's diameter, width, sidewall, circumference, and revolutions per mile measurements. You can even compare two different tires' measurements using our tire size comparison option.
Input Tire Dimensions
This is the 3-digit number displayed after the intended use code (P, LT, ST, or T). For
example: For P145/65R15, 215 would be the width in millimeters.
This is the 2-digit number before the "R" and after the "/". For example: For
P145/65R15, the aspect ratio would be 65.
This is the final number after the "R". For example: For P145/65R15, 15 would be the
diameter of the wheel the tire is designed to fit in inches.
0
0
0
0
0
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0Diameter
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0Width
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0Sidewall
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0Circ.
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0Rev./Mile
Alternative Sizes
| Tire Code | Diameter | Tire Width |
|---|
Disclaimer: These calculations are just estimates and are for informational purposes only. Alternative size suggestions are for reference only, and the options shown may not be exhaustive. We recommend that you verify these figures with the tire manufacturer for your specific tire and application.
How To Use Our Tire Size Calculator
To use our tire size conversion calculator, you'll need to know the basic tire measurements, which can be found in the tire code.
Single Tire Calculator
If you're looking for a basic tire diameter calculator that can show you other essential specs like tire width and circumference, follow these steps:
- Step 1: In the first box, enter the three-digit section width.
- Step 2: In the second box, enter the two- or three-digit aspect ratio.
- Step 3: In the third box, enter the one- or two-digit wheel diameter.
- Step 4: Hit the "Calculate" button and see the results.
Tire Comparison Calculator
If you're looking to see the measurements of two different tires side by side, you can use this option to see how each tire stacks up. Our calculator will even automatically show you the size differences.
- Step 1: Follow steps 1-3 in the section above for the first tire.
- Step 2: Follow those steps again for the second tire.
- Step 3: Hit the "Calculate" button to see the comparison chart.
When changing tire sizes, we recommend staying within 3% of the diameter/height of the original tire at most—any more than this and you could risk increased wear and tear or even brake failure.
Tire Sizes Explained
To use our calculator, you'll need to know the basics of how to read a tire size based on the tire size code printed on the sidewall.
How To Read Tire Sizes
To find your tire size, you'll need to look at the sidewall of your tire and look for the code printed in the largest size. It should be the leftmost code and should start with a letter, followed by a three-digit number, a backslash, and then two more two-digit numbers with a letter in the middle.
For example, for the Mickey Thompson Baja Legend MTZ Mud-Terrain 33" tire, the code would be P285/75R16. In this case, you'd be looking at the 285, the 75, and the 16 to enter into the calculator.
What the Tire Codes Mean
You might be surprised at how many different codes are included in just a handful of number and letter combinations. Here's what some of the key tire codes mean.
- Intended use: As the name suggests, this letter code tells you what the tires are meant to be used for: passenger vehicles (P), light trucks (LT), special trailers (ST), or temporary use (T).
- Section width: This three-digit number attached to the intended use code tells you the width of the tire in millimeters from sidewall to sidewall.
- Aspect ratio: After the backslash, the two- or three-digit number represents the sidewall's height to width ratio as a percentage. For 75, that means the distance between the rim and the outside of the tire is 75% of the tire's width.
- Tire construction: This letter tells you the tire's construction type: radial (R), diagonal (D), bias belt (B), or cross-ply (if no code is noted).
- Wheel diameter: Following the tire construction code, the final one- or two-digit number is the diameter/size of the rim in inches.
- Load index: The next code to the right of the size code is the load index, a two- or three-digit number that corresponds to an approved max weight load per tire. For 126, that means 3,748 pounds per tire.
- Speed rating: The letter attached to the load index is the speed rating, or the maximum speed the tire is rated to go when supporting weight that falls within the load index. The Q rating means 100 mph.
- USDOT code: Lower on the sidewall, you'll also see a USDOT (U.S. Department of Transportation) code, which tells you manufacturing information like the company, factory, and production date.
But these aren't all the codes. You can also see codes for things like approved extreme driving conditions, temperature grades, traction grades, max inflation pressure, whether the tire is tubeless, whether the tire is produced for a specific manufacturer, and much more.
How To Pick the Right Tire Size: 4 Things To Consider
Using the wrong tire size can lead to worsened handling, increased strain on your truck's suspension and transmission systems, and stress on its brake components. Having the wrong diameter can even affect your speedometer reading. It can also be just plain dangerous, so it's important to make sure you've got it right.
Here are a few common considerations when choosing tire sizes.
Changing Tire Size When You Change Rim Size
One of the most common reasons people change tire sizes is because they've upgraded their rims. A good rule of thumb is that the bigger the rim, the thinner the tire you can expect to need. That's because your wheel well doesn't get bigger to accommodate the extra space your rim and tire take up, so a thinner tire can help offset that.
That doesn't necessarily mean you need bigger rims in order to get bigger tires. You can potentially fit different sizes of tires onto the same rims, but as you probably guessed, bigger rims open up more tire size options.
How Tire Size Relates to Handling
In relation to tires, handling is all about where the rubber meets the road. Wider tires provide more surface contact with the road, leading to better handling. Meanwhile, diameter also leads to shorter braking distances but potentially slower acceleration. When it comes to the elements, however, more contact with the road can also mean higher likelihood of hydroplaning despite better dry-weather traction.
Should You Change All of Your Tires at the Same Time?
If all of your tires are heavily worn, you should replace them all at the same time. But if you have fairly new tires and get a single untimely flat, you can probably get by with replacing just one. If that's a front tire, it's a good idea to swap it with a rear tire. It's also OK to replace a pair of tires if one set wears out more quickly than the other—but the same rule applies, and you should put the new tires on the rear axle.
How Does Tire Size Affect the Speedometer and Odometer?
Bigger wheels translate to fewer rotations over the same distance. Since your speedometer measures your speed using the number of wheel rotations, if you increase your tire size, it'll think you're driving slower. The same goes for your odometer. It's a good idea to recalibrate your speedometer and odometer when you change tire sizes.
Closing Thoughts
Whether you're replacing your tires because you're hitting the trail, lifting your truck, updating your ride for the winter, or accommodating a new set of rims, stay as close as you can to factory-recommended sizing.
The above calculator should help you find tires that fit your truck or are compatible with new wheels. The comparison calculator should also help you see if another tire will be a good replacement option for your current tires.
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