Bolt circle calculator

Every hole's X and Y, ready to type into a DRO.

The formula

X = R × cos(θ) and Y = R × sin(θ), where R is half the bolt circle diameter and θ steps by 360 ÷ holes.

Coordinates are relative to the center of the circle, so add your part datum before typing them in. Angles run counter-clockwise from the positive X axis, which is the standard machine convention and matches G-code.

Getting the first hole where you want it

Start angle is the one input people skip. A six hole pattern at 0° puts the first hole at three o'clock; if the print shows a hole straight up, set the start angle to 90°. Getting this wrong rotates the whole pattern, which on a flange with a keyway or a marked orientation is scrap.

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