Bolt Circle Calculator

Bolt Circle Calculator for CNC, CAD, and Drilling Layouts

The Bolt Circle Calculator computes XY coordinates for equally spaced bolt holes on a circular pattern. Enter hole count, bolt circle radius, first hole angle, and optional center offset. Results update instantly for machining, CAD layout, or g-code programming.

Bolt pattern equations

For hole $i$ starting at index 1, with angle step $B = 360° / n$:

$$x_i = \cos((i - 1) \times B + A) \times R + x_c$$

$$y_i = \sin((i - 1) \times B + A) \times R + y_c$$

Where $n$ is hole count, $R$ is bolt circle radius, $A$ is first hole angle, and $(x_c, y_c)$ is center offset.

Related tools: Bolt Torque Calculator and Angle Cut Calculator.

Frequently Asked Questions

What is a bolt circle?

A bolt circle is the circular path that passes through the centers of all bolt holes in a flange or plate. Its radius defines how far each hole sits from the pattern center.

How do I set the first hole angle?

Measure the angle from the positive X axis (horizontal right) to the first hole. Use 0° when the first hole sits on the right side of the circle.

Can I export coordinates for CNC?

Yes. Copy or download the coordinate table from the tool output. Most CAM and CNC workflows accept comma-separated X/Y values or can import CSV data.

Does offset shift the whole pattern?

Yes. The center offset moves every hole by the same $(x_c, y_c)$ translation without changing spacing or radius.

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