Generate precise X/Y coordinates for any bolt hole circle (PCD). Standard for CNC machining, flanges, and wheel patterns.
A bolt circle — also called a pitch circle diameter (PCD) — is the imaginary circle that passes through the center of all holes in a circular pattern. Bolt circles are everywhere: wheel lug patterns, flange bolt patterns, bearing housings, motor mounts, and machine tool mounts. Our calculator generates the precise X/Y coordinates for any number of equally spaced holes, which you can input directly into a CNC controller or use for manual layout.
Where (Cx, Cy) is the center point, R is the bolt circle radius (PCD ÷ 2), and θ is the angle for each hole. The first hole is placed at the start angle; subsequent holes are spaced at 360° ÷ number of holes. For a 5-bolt pattern, the angular spacing is 72°.
The start angle determines where the first hole is placed relative to the center. For automotive wheel patterns, the convention is to place the first hole at 0° (3 o’clock position) and measure counterclockwise. For NEMA motor mounts, the first hole is typically at 90° (12 o’clock). Our calculator lets you set any start angle to match your specific application.
The straight-line distance between adjacent holes (the chord) is useful for layout verification. The formula is:
Where N is the number of holes. For a 5-bolt pattern on a 4-inch PCD, the chord is 2.351 inches. Measuring this distance between hole centers is the fastest way to verify your layout matches the design.
If you are measuring an existing wheel, count the lug holes and measure from the center of one hole to the center of the opposite hole (for even counts) or use the chord measurement formula. Common PCDs include 4x100mm, 4x108mm, 5x114.3mm, 5x120mm, and 6x139.7mm. Getting this wrong means the wheel simply will not fit.
For CNC programming, enter the coordinates as G-code positions (G81–G89 canned cycles or individual G0/G1 moves). For manual layout on a drill press or mill, transfer the coordinates to the workpiece using a height gauge or scribe. Our calculator outputs coordinates in inches — multiply by 25.4 for millimeters if your CNC uses metric.
If you are building a motor mount or machine fixture, verify the spindle motor wiring with our wire size calculator. For machining the part itself, use our speeds and feeds calculator to set the correct RPM and feed rate for your material.
Coordinates are calculated for equally spaced holes only. For irregular patterns (for example, a keyed bolt circle with one missing hole), calculate each position individually using the angle offset method.