Bolt Circle Calculator

How the coordinates are generated

Evenly spacing N holes around a circle means each hole sits 360°÷N apart from the next, starting from whatever angle you choose. Standard trigonometry converts each hole's angle to a position: X = radius × cos(angle), Y = radius × sin(angle), measured from the circle's center using the standard math convention where 0° points to 3 o'clock and angles increase counterclockwise — set the starting angle to 90 for the first hole straight up at 12 o'clock, which is the most common layout convention.

Using this on a manual mill vs. a CNC

On a manual mill with a DRO, these X/Y values are exactly what you dial in from the bore's center for each hole, one at a time. On a CNC, most controls and CAM software have a built-in bolt-hole-circle canned cycle that does this same math internally — this calculator is most useful for checking a canned cycle's output, programming a control that lacks the cycle, or laying out a pattern by hand before it ever reaches a machine.

Odd hole counts still divide evenly

The 360°÷N spacing works identically whether N is even or odd — a 5-hole or 7-hole pattern is just as evenly spaced as a 4-hole or 6-hole one, even though it won't have the left-right symmetry an even count gives you. If a print calls for a specific hole to land at a particular clock position, adjust the starting angle rather than trying to reorder the hole list.