Pitch circle diameter (PCD) is the diameter of an imaginary circle drawn through the center of a set of equally spaced holes or points arranged in a circular pattern. In everyday use, you’ll encounter this term most often when shopping for wheels, where it describes the bolt pattern that attaches a wheel to a vehicle’s hub. It also plays a key role in mechanical engineering, where it defines how gear teeth mesh together.
PCD in Wheel Fitment
When applied to vehicles, PCD refers to the diameter of the circle that passes through the center of every lug bolt hole on a wheel or hub. It’s always paired with the number of bolts, written in a format like 5×114.3. The first number (5) is the count of mounting holes, and the second number (114.3) is the PCD in millimeters. A car with a 5×120 bolt pattern has five lug holes arranged on a circle 120 mm across.
Older and American-market vehicles often use imperial measurements. A pattern described as “five on four and a half” is the same as 5×114.3 mm. Metric and imperial notations describe the same physical measurement, just in different units. You’ll see both formats used interchangeably in wheel catalogs and fitment guides.
Common PCD Sizes
Most passenger cars use 4-lug or 5-lug patterns. Common 4-lug sizes include 4×100 (many compact cars), 4×108, and 4×114.3. For 5-lug vehicles, the most widespread PCDs are 5×100, 5×112, 5×114.3, and 5×120. Trucks and SUVs sometimes use 6-lug or 8-lug patterns with larger diameters like 6×139.7.
Two PCDs can look very similar on paper but still be incompatible. For example, 5×112 and 5×114.3 differ by only 2.3 mm, yet a wheel designed for one will not seat correctly on the other. That small gap is enough to prevent the lug bolts from centering properly in their holes.
How to Measure PCD
The method depends on whether your wheel has an even or odd number of bolt holes.
On a 4-lug or 6-lug wheel, you can measure straight across from the inside edge of one hole to the outside edge of the hole directly opposite. That distance is the PCD, because the two holes sit on exact opposite ends of the circle’s diameter.
On a 5-lug wheel, no two holes sit directly opposite each other, so a straight-across measurement won’t work. Instead, measure the center-to-center distance between two adjacent studs (call that distance S), then divide by 0.5878. So if two neighboring studs are 67.2 mm apart, the PCD is 67.2 รท 0.5878, which equals roughly 114.3 mm. The equivalent formulas for other patterns: divide S by 0.7071 for 4-stud, and divide S by 0.5 for 6-stud.
Dedicated PCD gauges are available that handle 4, 5, 6, and 8-lug patterns and display results in both metric and imperial formats. A caliper works fine for a careful DIY measurement, but a purpose-built gauge removes the guesswork, especially on odd-numbered patterns.
Why Getting PCD Right Matters
Mounting a wheel with the wrong PCD is a safety issue, not just a fitment inconvenience. If the bolt holes don’t align precisely with the hub studs, the wheel can’t clamp flat against the hub face. That leads to uneven load on the studs, vibration at speed, and in a worst case, loosening or stud failure while driving. Even a 2 mm mismatch can create enough play to compromise braking stability.
Beyond safety, running a mismatched PCD can void the warranty on suspension and drivetrain components, since you’ve altered the wheel setup beyond manufacturer specifications.
Hub Centric Rings and PCD Adapters
It’s worth distinguishing PCD from centerbore, because the two get confused often. The centerbore is the large hole in the center of the wheel that sits over a raised lip on the hub. Hub centric rings fill the gap when a wheel’s centerbore is larger than the hub lip, keeping the wheel centered. They don’t change the bolt pattern at all.
PCD adapters are a different product entirely. These bolt onto the existing hub studs and provide a new set of studs on a different PCD, effectively converting one bolt pattern to another. They also space the wheel outward slightly, which changes the wheel’s offset. Quality adapters made from forged aluminum are considered safe for street use, but they add complexity and a potential failure point that a factory-matched PCD avoids.
PCD in Gears and Mechanical Design
Outside of wheels, pitch circle diameter is a foundational concept in gear engineering. Every gear has an imaginary pitch circle where its teeth effectively contact the teeth of a mating gear. The pitch diameter isn’t at the tip of the teeth or at their base. It sits partway between, at the point where force is actually transmitted between two meshing gears.
When two gears mesh correctly, the distance between their centers equals half the sum of their two pitch diameters. Engineers use this relationship to design gear trains with precise spacing. For gears on parallel shafts, the pitch diameter can be calculated directly from the center distance and the number of teeth on each gear, making it one of the first values determined in a gear design.
The same principle extends to any engineering layout where components are arranged in a circle: flange bolt holes on pipes, mounting holes on bearing housings, or stud patterns on brake rotors. In every case, PCD is simply the diameter of the circle that passes through the centers of those equally spaced features.