Enter the bolt circle radius (or diameter), the number of holes, and a starting angle, and this returns the X/Y coordinate for every hole — ready to drop straight into your CNC program or layout.
Bolt circle pattern
| Hole # | Angle (°) | X (in) | Y (in) |
|---|
Coordinates are relative to the bolt circle center at (0,0). Add your part’s center offset to use these directly as work coordinates.
How it works
Holes are spaced evenly around the circle: angle step = 360° / number of holes. For hole i (0-indexed), angle = starting angle + i × step. Then X = radius × cos(angle), Y = radius × sin(angle), using standard CCW-from-positive-X-axis convention — the same convention most CAM and CNC controls use for polar coordinates.
Chord spacing is the straight-line distance between adjacent holes: chord = 2 × radius × sin(180° / number of holes). Use it to sanity-check a layout with calipers, or to verify minimum hole edge distance.
Common bolt patterns
4-bolt and 6-bolt circles are the most common on flanges, pumps, and standard hardware. 3-bolt patterns show up on smaller fittings. For odd numbers of holes or non-uniform spacing, set the starting angle to put the first hole exactly where your reference feature is, then read off the rest.
FAQ
Which way does the starting angle point? 0° is along the positive X axis (3 o’clock), increasing counter-clockwise — the same convention G-code G02/G03 and most CAD/CAM tools use.
How do I get clock positions instead? Treat 12 o’clock as 90° and go clockwise from there, or just read the X/Y pairs directly — clock positions are rarely precise enough for machining anyway.
Can I use diameter instead of radius? Yes — halve your bolt circle diameter and enter that as the radius.
Related Guides
Dimensions & Geometry Calculators · Setup & Workholding Calculators · G-Code & CNC Calculators