Bolt circle calculator
Generate equally spaced hole-centre coordinates from a circle diameter. Set the first angle, numbering direction and centre offset.
1–360 equally spaced centres. Start angles can be −360,000 to 360,000 degrees and are normalized to 0–360 degrees. Extremely small circles relative to a large centre offset are rejected to avoid numeric precision loss. Change the input or settings to update your result. Results update as you type. Up to 1,000,000 characters.
Your result
How to use Bolt circle calculator
- Set circle diameter, unit and number of equally spaced centres.
- Choose the first angle, direction and centre coordinates.
- Review the diagram and download the full coordinate CSV or SVG.
Useful next steps
Set the circle and coordinate system
Enter the diameter of the circle passing through the hole centres. Zero degrees points right along positive X. Positive Y points up. Coordinates use the selected unit and are shifted by your entered centre X and Y values.
Choose where numbering begins
The first angle sets hole 1. Counterclockwise order increases each angle; clockwise order decreases it. Spacing is 360 degrees divided by the number of centres. Four centres on a 100 mm diameter circle, starting at zero around the origin, are (50, 0), (0, 50), (−50, 0) and (0, −50) mm.
Check the table and diagram together
The CSV contains every hole number, angle and coordinate in generated order. The SVG shows the same mathematical orientation. Markers represent centres only: their drawn size is not a hole diameter, and the schematic is not a full-size drilling template.
Download the coordinate list
Save the CSV, SVG or calculation report locally. Hole size, edge distance, machining tolerances, fastener choice and strength are not evaluated. Check coordinate conventions against the equipment or drawing that will use the numbers.