Compute evenly spaced hole positions on a bolt circle (PCD/BCD) for flanges, hubs, and fixtures. Supports metric/imperial, start angle, datum reference, and adjustable precision. Preview the pattern, export a clean PDF, or email results to your team.
Enter PCD, number of holes, start angle, datum (center/edge), unit & precision.
Click Calculate to get polar and Cartesian (X/Y) coordinates with a quick preview.
Export PDF or Send to Email. Need parts made? Get a Quote—we’ll attach your settings.
CAM programming & jig/drilling setup sheets (units and precision included in the export)
CMM/QC checkpoints using absolute X/Y to avoid chain error
Share a clean PDF/CSV with your machinist for quick review
Common (metric): PCD = 100 mm, Holes = 6, Start = 0°
Inch 5-lug: PCD = 4 in, Holes = 5, Start = 18° (5-on-5)
Tight pattern: PCD = 72 mm, Holes = 8, Start = 22.5°
Automotive example: 5×114.3 (PCD 114.3 mm), Holes = 5, Start = 18°
Tip: For machining and QC, use the absolute X/Y coordinates from the table rather than chaining distances—this minimizes accumulated error.
Purpose: This tool is designed to calculate the precise coordinates and orientation angles of holes evenly spaced on a bolt hole circle. It is intended for preliminary design and reference purposes only.
Input Requirements:
Circle Diameter: Must be a positive number representing the diameter of the bolt hole circle.
Number of Holes: Must be a positive integer greater than zero.
Starting Angle: Angle in degrees from the reference direction (usually the positive X-axis). Can be any real number; values will be normalized between 0° and 360°.
Direction: Choose clockwise or counterclockwise hole arrangement around the circle.
Center Coordinates (X₀, Y₀): The center of the bolt hole circle in the selected unit system.
Unit Conversion: Supports millimeters (mm) and inches (inch). When switching units, input values will be converted automatically. Ensure consistency when inputting dimensions.
Output Details:
Displays the X and Y coordinates of each hole relative to the specified center.
Shows the orientation angle of each hole, which indicates its angular position on the circle.
Assumptions & Limitations:
The tool assumes holes are perfect circles placed on a perfect circle. It does not support elliptical or other shaped holes.
Orientation angles are for reference only; for circular holes, orientation does not affect the hole shape.
This calculator does not generate CAD files or drilling templates. Use outputs as coordinate references.
Environmental factors, manufacturing tolerances, and material considerations are outside the scope of this tool.
Usage Recommendations:
Double-check all input parameters before calculation.
Use the output coordinates to assist in CAD modeling or CNC programming.
For detailed manufacturing drawings, consult with design engineers or CAM specialists.
Disclaimer:
The results provided are approximate and for guidance purposes. Actual manufacturing requirements may vary and should be verified by qualified personnel.
Need parts made from these specs? Get a same-day quote — we’ll attach your current settings.
Related Tools
Hole Spacing Calculator → /tools/hole-spacing
Tap Drill Size & Thread Engagement → /tools/tap-drill-size
Tolerance Fit Helper (ISO 286 + IT5–IT16) → /tools/tolerance-fit-helper
Material Weight Calculator → /tools/material-weight-calculator
Q1. How accurate are the coordinates?
Analytical geometry with rounding to your selected decimals. For production, apply drawing tolerances and verify on a test piece.
Q2. Why provide both polar and X/Y?
Different CAM and QC workflows prefer different formats. We include both to avoid re-calculation.
Q3. What start angle for 5-bolt patterns?
Use 18° for symmetric 5-on-5 inch patterns; verify against your flange/hub design.
Q4. Can I set a non-center datum?
Yes. Use an edge-based datum with a known center offset; annotate the datum on the exported PDF.
Q5. Are units consistent in the PDF?
Yes. If you switch units, re-export to avoid mixed-unit confusion.
Q6. Can I include center coordinates (X₀, Y₀)?
Yes. Define the center in your selected units; all outputs are relative to that center.
Q7. Can this feed CAD/CAM?
Copy the X/Y table (text/CSV) or attach the PDF to your setup sheet; many CAM posts accept CSV imports.
Q8. Can you quote my part from these results?
Yes. Click Get a Quote, add quantity/material/finish, and we’ll reply with a price range & lead time.
