Bolt Circle Calculator: Hole Coordinates & PCD

Published September 22, 2026 · MfgWorkbench editorial reference

Lay out equally spaced holes on a pitch circle. Enter a diameter, a whole-number hole count and a start angle to get coordinates relative to the circle center.

Coordinate convention and formulas

The origin is the center of the pattern. Positive X points right; positive Y points up. Angles increase counterclockwise from positive X. The red point in the diagram identifies hole 1. Select either millimeters or inches and keep the drawing in that same unit; the tool does not convert an existing input when the unit label changes.

For N holes on diameter D, the angular spacing is 360°/N. Hole i is at θ = θ₀ + (i − 1) × 360°/N, with X = (D/2) cos θ and Y = (D/2) sin θ. Adjacent-hole center distance is D sin(180°/N). These are center coordinates, not the outer edge of a drilled hole.

Example: six holes on a 100 mm PCD

At a 0° start angle, hole 1 is (50, 0) mm, hole 2 is (25, 43.301270) mm and hole 3 is (−25, 43.301270) mm. The remaining holes mirror those positions around the origin. Angular spacing is 60° and adjacent centers are 50 mm apart. If the pattern is centered at machine position (120, 80), add 120 to every X result and 80 to every Y result.

Before transferring coordinates to a drawing or machine

Confirm the viewing direction: a pattern viewed from the opposite face may appear mirrored. Check whether the drawing locates a hole on an axis or halfway between axes. Changing the start angle rotates the whole pattern; changing hole diameter does not change PCD.

The CSV is a coordinate reference, not machine code. Verify work offsets, tool clearance, part orientation and tolerances separately. For an existing pattern, an adjacent center distance c gives D = c/sin(180°/N); measuring across outside edges of holes will overstate c unless hole size is accounted for.