Start AutoCheck
Tire Size Calculator

Tire Size Calculator

Calculate your tire size specifications including diameter, circumference, revolutions per mile, and more.

Sidewall code helper

Enter Tire Size

Use the three numbers printed on the tire sidewall. The example below breaks down what each part means.

225 / 45 R 18
Width Tire section width from sidewall to sidewall, measured in millimeters.
Aspect ratio Sidewall height as a percentage of the tire width.
Wheel diameter The rim size the tire fits, measured in inches.
Tire size parts diagram A tire diagram labeling section width, sidewall height, and wheel diameter. Width Sidewall Wheel / Rim
mm
Example: 225 means the tire is 225 mm wide.
%
Example: 45 means sidewall height is 45% of width.
in
Example: R18 fits an 18-inch wheel.