Bolt Circle Calculator

A bolt circle (also called PCD - Pitch Circle Diameter) is an imaginary circle that passes through the center of all bolt holes in a circular pattern. It is defined by two measurements: the number of bolts and the diameter of the circle they lie on. Common examples include 5×100mm (5 bolts on a 100mm circle) for wheels, 4×4.5" for trailer wheels, and various patterns for flanges, flywheels, and other mechanical components. The PCD determines compatibility between components.

For even-numbered bolt patterns (4, 6, 8 bolts): Measure from the center of one bolt hole directly across to the center of the opposite bolt hole. This is the PCD. For odd-numbered patterns (5 bolts): Measure from the center of one bolt hole to the center of the second hole next to it (not the one across). Then multiply by 1.701 to get the PCD. Alternatively, measure the distance between two adjacent bolt centers and use: PCD = d / sin(180°/n), where d is adjacent bolt distance and n is number of bolts.

Common wheel bolt patterns: 4×100mm (Honda Civic, Mazda Miata), 4×108mm (Ford Focus, Volvo), 5×100mm (Subaru Impreza, VW Golf), 5×112mm (Mercedes, Audi, BMW), 5×114.3mm (Toyota Camry, Honda Accord, Nissan Altima), 5×120mm (BMW 3/5 Series), 5×4.5" (Ford Mustang, Jeep Wrangler), 6×5.5" (Ford F-150, Chevy Silverado), 8×170mm (Ford Super Duty). Always verify your vehicle's specific pattern - using the wrong PCD is dangerous.

Accurate bolt circle measurement is critical for safety and proper function. If the bolt circle is wrong: Wheel lug nuts won't seat properly (dangerous), flange bolts may not align, causing leaks in pipe flanges, excessive vibration and wear on components, uneven load distribution causing bolt failure, and potential catastrophic failure of the assembly. Always use accurate measurements - calipers are preferred over tape measures. When in doubt, consult the manufacturer specifications rather than measuring.