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 different places you’ll be able to find your vehicle’s tire size, including:

  1. Owner’s manual
  2. Driver’s side door jamb
  3. Inside your glove box door
  4. Within your gas tank hatch
  5. 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. 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

While our tire size calculator provides a good visual representation of differing tire sizes, we further explain alphanumeric tire size codes below:

DimensionsDefinitionHow To CalculateMath
WidthThe width of a tire's tread pattern275.0 millimeters divided by
25.4 to get width in inches
275 ÷ 25.4 = 10.827
Sidewall HeightThe height of the sidewall measured from wheel rim to the top of the tire's treadAspect ratio divided by 100,
then multiplied by section width
275 x (60 ÷ 100) = 165
DiameterThe total diameter measuring one side of a tire to anotherThe number following R added
together with the product of
the sidewall height multiplied by 2
20 + (6.496 x 2) = 32.992
CircumferenceThe distance around the outside of a tireDiameter multiplied by pi20 x 3.14 = 62.8
Revolutions/MileThe number of times a tire rotates in one mile63,360 divided by circumference63,360 ÷ 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 and tire expert, Jonathan Benson of, to tell us some over-arching characteristics to look for when buying new tires:

“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’s 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 continues on to to note that especially in the U.S., where you live and drive plays a huge role in what to look for when buying tires. As he quite rightly points out, drivers in Utah and South Carolina will be looking for two completely different types of tires.

*Data accurate at time of publication.