Bolt Circle Calculator
X/Y coordinates for equally spaced bolts on a bolt circle, plotted to scale.
What is Bolt Circle?
A bolt circle is a set of holes on a common circle — a flange, a wheel hub, a bearing housing. The drawing gives the bolt circle diameter and the bolt count; the mill or the drill needs coordinates, and the machinist needs to see the pattern before trusting it. The chord between adjacent bolts is the number a caliper checks, and it is not the same as the arc length between them.
How it works
Each bolt sits at the start angle plus a multiple of 360° ÷ n, at a radius of half the bolt circle diameter, so its coordinates are R·cos θ and R·sin θ. Angles are measured anticlockwise from the 3 o'clock position, the convention a drawing uses. The page plots the pattern to scale with equal x and y spacing (so the circle is a circle), numbers each bolt, and prints the chord, the circumference and the arc length per bolt alongside the coordinate table.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.