Bolt Circle Calculator
X–Y coordinates of equally spaced holes on a bolt circle (PCD) with any centre, start angle and arc span, plus the chord between holes, G-code and a drawing.
A table of hole angles and coordinates, the angular pitch and the chord for a caliper check, a copyable G-code-style position list, and an SVG of the pattern.
Example: 6 holes on a Ø100 PCD from 0°: holes at (50, 0), (25, 43.301), (−25, 43.301), (−50, 0) … 60° apart with a 50 mm chord; 5 holes over a 120° arc sit 30° apart with a hole at each end.
Polar to Cartesian,
hole by hole.
The convention, the arc option, and what the chord is for.
Coordinates
Hole k of N sits at angle θ = start + k × 360°/N from +X, counter-clockwise, and at x = cx + (D/2)·cos θ, y = cy + (D/2)·sin θ from the pattern centre, D being the pitch circle diameter. That is the CAD and CNC convention (Y up); a drawing that measures clockwise from +Y, or a screen with Y down, needs a mirror.
Arcs and G-code
For a partial pattern the span is divided by N − 1 so there is a hole at each end of the arc. The G-code-style list is just the X/Y pairs with a G20/G21 line; drop it into a drilling cycle. Coordinates are rounded to the decimals you set, with negative zero suppressed.
Chord
Adjacent holes are 2·(D/2)·sin(pitch/2) apart centre to centre — the number a caliper can check on the finished part; when the chord is smaller than the hole diameter the holes overlap and the page says so. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- x = cx + (D/2)·cos θ, y = cy + (D/2)·sin θ with θ = start + k·360°/N (or span ÷ (N − 1) on an arc); chord = 2·(D/2)·sin(pitch/2); angles counter-clockwise from +X
Last reviewed 20 September 2026. How results are checked: How we verify.