FREE ENGINEERING TOOLS · FORMULAS & REFERENCES
Bolt Circle Calculator: PCD, Hole Coordinates & CSV
Generate equally spaced hole X/Y coordinates, adjacent-hole spacing and a layout from pitch circle diameter, hole count, start angle and center. Download CSV; supports clockwise/counterclockwise and mm/inches.
Enter parameters
Load an example:
Calculated results
Parameters changed. Recalculate before viewing or exporting results.
| Pitch circle radius | 50 mm |
|---|---|
| Angular step | 60 ° |
| Adjacent-hole center distance | 50 mm |
| Hole | Angle (°) | X (mm) | Y (mm) |
|---|---|---|---|
| 1 | 0 | 50 | 0 |
| 2 | 60 | 25 | 43.30127019 |
| 3 | 120 | -25 | 43.30127019 |
| 4 | 180 | -50 | 0 |
| 5 | 240 | -25 | -43.30127019 |
| 6 | 300 | 25 | -43.30127019 |
PCD is the diameter through the hole centers. Zero degrees points along +X, with +Y upward. Hole diameter, cutter radius and machine compensation are excluded.
Calculation formulas
θi = θ0 ± i·360°/N · Xi = Xc + (PCD/2)cos θi · Yi = Yc + (PCD/2)sin θi · chord = PCD·sin(π/N)
How does PCD differ from hole spacing?
PCD is the diameter of the circle through all hole centers. Adjacent-hole distance is a straight chord. For six equal divisions the chord equals the radius, but this is not generally true. At 100 mm PCD, six holes have 50 mm spacing; four holes have about 70.7107 mm spacing.
How are start angle and direction defined?
The start angle locates hole 1; subsequent holes add or subtract 360°/N. The start angle itself always uses +X as zero and counterclockwise as positive. Clockwise only changes the ordering of later holes. Output angles are normalized to 0–360°.
Are these coordinates a machine program?
These are coordinates, not a complete program. They do not define the work coordinate system, Z depth, tool, feed or compensation. CSV is intended for checking and import preparation; verify the drawing and machine setup before machining.
What do the CSV and drawing contain?
CSV contains hole number, angle, X, Y and units in table order. The drawing shows positions and order; the dots do not represent physical hole diameters. Recalculate after changing parameters before exporting updated results.