Pitch circle diameter (PCD) is the diameter of the circle that the wheel studs form.

How to calculate the PCD 

Measure the distance between two adjacent studs (measure from the centre point of the studs). Once you have this measurement, use the formulas below to calculate the PCD.

The measurement between the two studs is indicated as ‘S’ in the following diagrams and formulas.

Formulas 

3 Stud PCD = ‘S’ / 1.155

4 Stud PCD = ‘S’ / 0.7071

5 Stud PCD = ‘S’ / 0.5878

6 Stud PCD = ‘S’ / 0.5

8 Stud PCD = ‘S’ / 2.613

Tips 

You can also measure a 4, 6 and 8 stud PCD by measuring from the centre of a stud to the centre of the stud directly opposite. For odd numbered stud PCDs if you imagine the circle running through the centre of the studs (as shown above). Measure from the centre of a stud to where the circle line would be directly opposite. However, this technique may not be as mm accurate, so bear this in mind when buying your wheel.