How to Use Bolt Circle Calculator
The Bolt Circle Calculator generates a ready-to-use hole list.
- Pick a unit — mm or inch.
- Enter the PCD or radius — Either dimension works; the calculator converts internally.
- Enter number of holes and start angle — Plus optional centre coordinates.
- Read the result — A table of hole X / Y coordinates and chord distance.
Formula & Theory — Bolt Circle Calculator
The Bolt Circle Calculator uses polar-to-Cartesian conversion:
θ_i = start + 360° × i / n
x_i = cx + R × cos(θ_i)
y_i = cy + R × sin(θ_i)
chord = 2 × R × sin(π / n)| Symbol | Meaning |
|---|---|
| R | Pitch radius (PCD / 2) |
| n | Number of holes |
| start | Start angle for the first hole |
| cx, cy | Centre of the bolt circle |
| chord | Distance between adjacent holes |
Hole position tolerance
A perfectly calculated bolt circle still needs an inspection step: combine these coordinates with a True Position Calculator to verify the as-built pattern.
Use Cases for Bolt Circle Calculator
- Wheel and hub design — Lay out lug-bolt circles for automotive and trailer wheels.
- Flange manufacturing — Generate hole patterns for pipe flanges and gasket fits.
- Rotary equipment — Position motor mount holes, encoder bolts and brake disc patterns.
- CNC programming — Paste coordinates directly into your post-processor or DXF.
- Education — Demonstrate polar coordinates with a concrete engineering example.
- Inspection — Cross-check measured pattern against the calculated nominal.
A clean coordinate list saves you from layout errors. The Bolt Circle Calculator delivers exactly that.