Fabrication calculator
Flange hole marking calculator
Calculate equal hole spacing on a pitch circle: angular pitch, chord distance and individual hole angles.
Angular pitch—degrees
Chord between centres—mm
Half-pitch / straddle angle—degrees
| Hole | Angle | X from centre | Y from centre |
|---|
Reference only. Confirm orientation, clocking and drilling against the approved fabrication drawing. Coordinate values use the flange centre as 0,0.
FAQ
Common questions
How is equal flange hole spacing calculated?
For N equally spaced holes on a pitch circle diameter PCD, the angular pitch is 360°/N and the straight-line chord between adjacent hole centres is PCD × sin(180°/N).
What is a straddle angle?
For symmetric bolt-hole layout around a centreline, a common starting offset is half the angular pitch, or 180°/N. Always follow the drawing or applicable standard.
Can I enter inches?
Yes. Select inches and the calculator preserves the selected unit for PCD and chord distance. Angles are always shown in degrees.