Tire Size Calculator
Motor1 Reviews Team Take:
- A tire size calculator can help you understand the difference in tire sizes and explain their alphanumeric codes. Use this free tool before buying your next set of tires.
- To read your recommended tire size, you can look at your owner’s manual, driver’s side door, or gas tank hatch.
- When buying new tires, you’ll want to consider the terrain you frequently drive on, weather conditions, and the kind of driving experience you’re looking for.
Struggling to figure out what size tire you need? Car tire size is typically indicated by an alphanumeric code. Being able to read and understand this code is incredibly important, especially if you’re looking at purchasing a new set of tires.
Tire Size Calculator
How to Read Tire Size
Regardless of what kind of vehicle you drive, finding your tire’s size is relatively easy. There are five places you’ll be able to find your vehicle’s tire size, including:
- Owner’s manual
- Driver’s side door jamb
- Inside your glove box door
- Within your gas tank hatch
- On your tire’s sidewall
Most people settle on simply reading the tire’s sidewall, but you’ll need to be able to decipher the code displayed there. For most vehicles, you’ll see the letter “P” before the code’s sequence begins. The tire size code is a series of numbers that represent width, aspect ratio, and rim diameter—in that order.
Example Tire Size Code: 275/60R20
Explanation: 275 refers to section width, 60 refers to aspect ratio, and 20 refers to rim diameter
Here’s a more in-depth breakdown of alphanumeric tire size codes:
| Dimensions | Definition | How to Calculate | Math |
|---|---|---|---|
|
Width |
The width of a tire’s tread pattern |
275.0 millimeters divided by 25.4 to get width in inches |
275 ÷ 25.4 = 10.827 |
|
Sidewall Height |
The height of the sidewall measured from wheel rim to the top of the tire’s tread |
Aspect ratio divided by 100, then multiplied by section width |
275 x (60 ÷ 100) = 165 |
|
Diameter |
The distance spanning the two bead seats (where the tire mounts to the rim) |
The number following R added together with the product of the sidewall height multiplied by 2 |
20 + (6.496 x 2) = 32.992 |
|
Circumference |
The distance around the outside of a tire |
Diameter multiplied by pi |
20 x 3.14 = 62.8 |
|
Revolutions/Mile |
The number of times a tire rotates in one mile |
63,360 divided by circumference |
63,360 ÷ 62.8 = 1,008.917 |
It should be noted that for this example, sidewall height is indicated in millimeters (MM) and needs to be converted to inches in order to calculate diameter (6.496 in this case).
What to Look for When Buying Tires
We conferred with our independent tire tester, Jonathan Benson of TyreReviews.com, to discuss what to look for when buying new tires. Here’s what he had to say:
“I think one of the most important things you need to learn or realize about tires is that every tire is a compromise. There is no such thing as the perfect tire—though some manufacturers might claim it. But there are definitely some trade-offs in tire performance. So things like wet grip versus rolling resistance or energy use—they’re quite often a trade-off.”
He notes that especially in the United States, your driving environment plays a huge role in what to look for when buying tires.
For example, drivers in Utah and South Carolina will be looking for two completely different types of tires due to drastically different weather conditions. A driver in Utah may need to invest in a set of winter tires to have better traction on snow-covered roads. Motorists in South Carolina likely won’t need snow traction and thus a set of all-season tires makes sense. People who frequently travel on gravel roads might benefit from all-terrain tires. Sports car owners who only embark on fair-weather drives might find high-performance summer tires are the best fit.
How To Read A Tire
Tire sizes aren’t the only informative codes added to tires. You may have noticed there are two markings following the tire size, a number and a letter. The number represents the tire’s load index while the latter represents its speed rating.
Tire Speed Rating Chart
A tire’s speed rating is easy to understand. It indicates the top speed a tire can safely get to. Below, we display tire speed ratings (mostly in alphabetical order) and the indicated speed they represent in miles per hour (mph):
