The bolt pattern is made up of the number of bolts and the diameter of the imaginary circle they create (BCD). The BCD can be expressed in inches or millimeters. Bolt patterns with an even number of bolts are measured from bolt center to bolt center. 5 lug bolt patterns are measured from the center of the upper bolt to the bottom of the lower bolts.
A bolt pattern is expressed as follows:
Where N = number of bolts and BCD = bolt center diameter.
For example, if you have a 5 lug wheel and your bolt center measures 114.3 millimeters then your bolt pattern is 5×114.3.