Manufacturing · Layout

PCD Calculator

Lay out equally spaced holes on a pitch circle — dial in PCD, count, and start angle, then watch the bolt-circle diagram and coordinates update live.

Bolt circle layout
Equally spaced holes on a pitch circle — set center, PCD, count, and first-hole angle.
Cx
Cy
PCD
Ø

Used for the live diagram only — does not change coordinate math.

N
Common counts
θ₀

Angle of the first hole, counterclockwise from the positive X-axis (degrees).

Live bolt-circle preview

Enter a positive PCD, hole diameter, and hole count to preview the pattern.

Result

Hole coordinates

θᵢ = θ₀ + i · (360° / N)

N
—

Set PCD and hole count — the bolt-circle diagram updates as your pattern takes shape.

About pitch circle diameter

Bolt-circle geometry for flanges, wheels, sprockets, and CNC hole patterns.

PCD (pitch circle diameter) is the diameter of the imaginary circle through the center of every hole in a circular pattern. It defines bolt circles on flanges, wheel hubs, pulleys, and gear blanks — not the hole size itself, but where hole centers sit.

Each hole is placed at equal angular spacing. The start angle sets where hole 1 lands, measured counterclockwise from the positive X-axis.

  • Angle θᵢ

    θᵢ = Start Angle + i × (360° / N)

    N is the number of holes; i = 0 … N−1.

  • X coordinate

    xᵢ = Cx + (PCD / 2) × cos(θᵢ)

    Cx is the circle center X; θᵢ in radians in code.

  • Y coordinate

    yᵢ = Cy + (PCD / 2) × sin(θᵢ)

    Cy is the circle center Y.

  • Holes are equally spaced around the PCD (360° / N between adjacent centers).
  • Start angle is CCW from +X, matching typical CAD and CNC coordinate conventions.
  • Hole diameter affects the diagram only; coordinates use pitch-circle centerlines.
  • Trigonometry uses radians internally: radians = degrees × (π / 180).
  • Use the decimal-place selector and CSV export to match drawing tolerance or CAM resolution.
  • Wheel and sprocket bolt patterns (4, 5, 6, or 8 studs).
  • Pipe flange drilling templates and gasket alignment.
  • CNC bolt-circle macros and probing routines.
  • Gear blank pin circles and indexer plate layouts.