Swapping tires isn’t a problem for most drivers especially if the old and new tire sizes are the same.

The need to calculate your tire size may arise for instance, when you buy a new car and wonder if it can use your old tires.

**Formula to calculate tire size.**

R is the rim size in inches.

H is the height

W is the width in millimeters and it is the first number to appear.

Wheel rim size (R) is multiplied by 25.4 to obtain the wheel rim size in millimeters.

**Example: **

Find the circumference for a tire with the 245/45 R 18 label.

Therefore, the tire size is 2,129 mm.