By Zencalcy Editorial TeamLast reviewed About us
A bolt circle is easiest to drill from coordinates rather than by stepping a divider around and accumulating error. Each hole sits at radius r and angle θ, with coordinates (r cos θ, r sin θ). This calculator lists every hole and the straight-line spacing between them.
Hole coordinates and spacing on a bolt circle.
x = r × cos θ, y = r × sin θ chord = 2 r sin(π ÷ n)
Angles increase counter-clockwise from the positive X axis. Most drawings use 0° at the top or at 3 o'clock — check the drawing's convention before drilling. Coordinates are relative to the circle centre.
| Symbol | Meaning |
|---|---|
| r | Bolt circle radius. |
| n | Number of holes. |
| θ | Angular step, 360° ÷ n. |
Each hole is 60° apart and the chord between adjacent holes is 5.00 inches; the first hole at 0° is at (5, 0).
Continue with the Angle Cut Calculator, Angle of Depression Calculator, Bowl Segment Calculator, or the Countersink Depth Calculator — or browse more layout & geometry and all construction calculators.
Mark the centre, scribe the circle, then step off the chord distance with dividers. The chord is 2r sin(180/n).
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026