To find the bolt pattern on a car you would need to measure the diameter of a circle drawn through each lug stud. On cars with an even number of lugs all that is necessary is to measure the distance from the center of one lug stud to the center of the lug stud directly opposite. On cars with an odd number of lug studs it becomes a bit more involved. However we have a relatively simple solution to solve this. You need to measure the distance from the center of a lug stud to the outside of an opposing lug stud (see diagram). This will give you a relatively accurate bolt circle diameter.