The 2003 BMW 530i Sedan bolt pattern is 5-120 mm. This means there are 5 lugs and the diameter of the circle that the lugs make up measures 120 mm or 4.72 inches across. To get a close measurement of your 5 lug bolt pattern without a bolt pattern tool you should measure from the center of one lug to the outer edge of the lug furthest from it.
