How to use the bolt pattern pcd calculator
- Enter the number of studs or bolts in the pattern, from 3 to 12.
- Choose what you measured: neighbor to neighbor, between the centers of two studs next to each other, or the farthest studs, which is straight across when the count is even.
- Enter the distance between those centers and pick millimeters or inches.
- Read the pitch circle diameter in both units and use the cross check for the other measurement.
Formula
PCD = distance / sin(k x 180 degrees / n)
k = 1 for neighbors, k = n / 2 rounded down for the farthest pair
neighbor distance = PCD x sin(180 degrees / n)
The studs sit at the corners of a regular polygon on a circle. The straight-line distance between two corners k steps apart is the diameter times the sine of k half-turns of the angle between corners.
A five stud pattern
A pattern with 5 studs on a 114.3 mm circle has neighbors 114.3 x sin(36 degrees) = 67.18 mm apart and farthest studs 114.3 x sin(72 degrees) = 108.71 mm apart. Measuring 67.2 mm between neighbors gives a PCD of 67.2 / sin(36 degrees) = 114.33 mm, which is 4.5 inches.
With 4 studs, the farthest pair is straight across, so a measurement of 100 mm across means a PCD of exactly 100 mm, and neighbors are 70.71 mm apart. With 6 studs, a neighbor distance of 2.5 inches means a PCD of 5 inches, or 127 mm.
Measuring carefully
Measure from the center of one stud hole to the center of the next. A caliper reads edges, so measure from the near edge of one hole to the far edge of the next, then subtract one hole diameter, or measure edge to edge on the near sides and add one hole diameter. For even counts, measuring straight across gives the PCD directly and is usually more accurate.
Checking against a part
Patterns are listed by number and PCD, for example 5 studs on 114.3 mm, but the real measurement can differ by a fraction of a millimeter. Compare the result with the part maker's listing and fit data before buying wheels or parts. See the Tire Size Calculator for tire dimensions and the Tire Life Calculator for wear.
Assumptions and limits
- All studs lie on one circle and are spaced evenly.
- The distance is measured center to center in a straight line.
- Offset, center bore and stud size are separate fitment details that are not covered.
- The tool does not name standard patterns.
Frequently asked questions
What is the pitch circle diameter?
It is the diameter of the circle that passes through the centers of all the studs or bolts. It is usually given with the number of studs, such as 5 on 114.3 mm.
How do I measure a five stud pattern?
Five studs have no stud directly across, so measure between the centers of two neighboring studs, or between a stud and the farthest one. The page handles both measurements.
Why is the answer a little different from a listed pattern?
A tape or caliper measurement has small errors, and the listed value is a round number. If the result is within a fraction of a millimeter of a listed pattern, the listed one is probably right.
Does the page support inches?
Yes. Pick inches for the measurement, and the result shows both millimeters and inches. One inch is exactly 25.4 millimeters.