bolt circle formula
θᵢ = θ₀ ± i·(360°/n); Xᵢ = Xc + (PCD/2)·cos(θᵢ); Yᵢ = Yc + (PCD/2)·sin(θᵢ). 0° = +X axis (3 o'clock). Use 90° if the drawing shows the first hole at the top.
Hole Circle Calculator (Bolt Circle/PCD)
X/Y coordinates, preview, CSV and G81/G83 G-code from the PCD, number of holes and start angle. Ideal for flanges and circular patterns without CAM.
Calculates the circular pattern (PCD/BCD): absolute and incremental coordinates, preview, CSV and G-code (Fanuc G81/G83, Siemens CYCLE81/83 or Heidenhain CYCL 200). 0° = +X axis (3 o'clock); 90° = first hole at the top.
Pattern
Angular pitch
60.0000°
Adjacent chord
50mm
Radius
50mm
PCD from chord
Measure center to center between two neighbouring holes and enter the total count.
85.065 mm
G-code CNC
(CIRCULO DE AGUJEROS / PCD - 6 agujeros) G21 G90 G17 M3 S1800 G0 Z5.000 G0 X50.000 Y0.000 G81 Z-10.000 R2.000 F120.000 X25.000 Y43.301 X-25.000 Y43.301 X-50.000 Y0.000 X-25.000 Y-43.301 X25.000 Y-43.301 G80 G0 Z5.000 M5 M30
Indicative Fanuc/ISO. Validate depths, plane and origin on your control. G/M codes
How to calculate a bolt circle without CAM
Get exact X/Y coordinates, preview, CSV and G-code (Fanuc G81/G83, Siemens CYCLE81/83 or Heidenhain CYCL 200) from the pitch circle diameter, the number of holes and the start angle. Made for programming flanges, covers and circular patterns without CAM.
From chord to PCD
If you measure the distance between neighbouring holes: PCD = C / sin(180°/n). Ideal for 5×… wheel rims or odd-count flanges where diametral caliper measurement is impossible.
From coordinates to machine
Copy the table, export CSV or generate your control's cycle. Open the program in the Viewer to check toolpath and cycle time before drilling.
Frequently asked questions
What is the PCD or BCD in a circle of holes?
PCD (Pitch Circle Diameter) and BCD (Bolt Circle Diameter) are the diameter of the imaginary circle passing through the center of all the holes. It is measured center to center, not edge to edge of the hole nor the flange's outer diameter.
How are the X/Y coordinates of each hole calculated?
With radius R = PCD/2 and angle θᵢ = θ₀ ± i·(360°/n): X = Xc + R·cos(θ), Y = Yc + R·sin(θ). The 0° angle is on the +X axis (3 o'clock); 90° places the first hole at the top (12 o'clock).
How do I get the PCD if I only measure the distance between two neighboring holes?
Measure the chord C (center to center) between two adjacent holes and use PCD = C / sin(180°/n), where n is the total number of holes. It is the usual method for 5- or 7-hole patterns where you cannot measure diametrally.
What direction of rotation should I use in CNC?
The meaning only changes the numbering order. In plane G17 seen from above, many programmers use counterclockwise (mathematical). Choose the one that matches the plan or the drilling order you want on the machine.
Can I generate G81 or G83 directly?
Yes. Choose the control and the cycle: Fanuc/Haas/ISO (G81/G83 or G0/G1), Siemens (MCALL CYCLE81/CYCLE83) or Heidenhain (CYCL DEF 200 + L … M99). Always check depths and the safety plane on your machine; you can open the program in the GetGCode Viewer.
mm or inches?
You can work in mm (G21) or inches (G20). All fields (PCD, center, Z, R, F) use the same unit. Do not mix units in the same calculation.
What are the dX and dY columns for?
They are increments from the previous hole (the first one with respect to the center). Useful in DRO or in G91 incremental programming if your control or workshop habit requires it.
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