⭕ Bolt Circle Patterns

Written and maintained by the PhDino author · Last reviewed 21 September 2026 · Checked against 2 independent reference calculations · how PhDino checks its numbers

Laying out evenly spaced holes around a circle for a flange, wheel, or mounting pattern.

A bolt circle (or bolt circle diameter, BCD) describes a set of holes spaced evenly around an imaginary circle — the standard way flanges, wheels, and mounting patterns distribute fasteners symmetrically around a center. Laying one out by hand comes down to basic circle geometry: divide the full circle evenly among the holes, then find the straight-line (chord) distance between adjacent holes for measuring or programming.

The angle between adjacent holes is simply 360° divided by the hole count — obvious once stated, but the chord distance (the actual straight-line spacing a caliper or CNC program needs) requires a bit of trigonometry, since it's not the same as the arc length along the circle's curve.

Key formula

Angle between holes = 360° ÷ number of holes
Chord distance = bolt circle diameter × sin(180° ÷ number of holes)

Notes & limitations

• This assumes holes are evenly spaced starting from an arbitrary reference angle — real-world patterns sometimes intentionally offset the first hole from straight up/down or from a keyway, which doesn't change the spacing math, just where the pattern starts.
• Standard automotive/wheel bolt patterns are conventionally described as "hole count × BCD" (e.g. 5×114.3mm) using exactly this geometry — this calculator works for any bolt circle, not just wheels.