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Tire Size Calculator

Tire Size Calculator & Speedometer Error | Fitment Guide by Vehicle

Calculate tire diameter, sidewall height, circumference & speedometer error (225/65R17, 265/70R17). Compare tire size changes & fitment risk before buying.

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.