Bolt circle calculator
Each hole sits at x = R·cos θ, y = R·sin θ with the angle stepping by 360°/count. Six holes on a Ø100 bolt circle starting at 0° land at (50, 0), (25, 43.301), (−25, 43.301), and so on. Enter the bolt-circle diameter, hole count, and start angle; the table gives every coordinate ready to copy into a DRO, program, or inspection report.
Pattern
CCW from +X (3 o'clock), whatever the numbering direction; blank = 0°
- Hole count
- Angle step α
- Chord, hole to hole c
How it’s calculated
X = R·cos(θ), Y = R·sin(θ), with θ advancing by 360° ÷ hole count from the start angle. CW reverses the sign of the angle step. Neighbouring centres are c = D·sin(180° ÷ hole count) apart.
Coordinates
| Hole # | Angle° | X (mm) | Y (mm) |
|---|---|---|---|
| 1 | 0.000 | 50.000 | 0.000 |
| 2 | 60.000 | 25.000 | 43.301 |
| 3 | 120.000 | -25.000 | 43.301 |
| 4 | 180.000 | -50.000 | 0.000 |
| 5 | 240.000 | -25.000 | -43.301 |
| 6 | 300.000 | 25.000 | -43.301 |
When do you compute bolt-circle coordinates?
A bolt-circle pattern is defined on the drawing by a diameter, a hole count, and a start angle — but a DRO, CNC program, or CMM wants each hole as an X/Y coordinate. This calculator does that conversion, stepping the angle by 360°/count from your start reference and resolving every hole to Cartesian coordinates about the pattern centre.
Use it to program a pattern from a callout, to lay out holes on a manual machine, or to check that measured hole positions match the intended circle. Set the start angle to match the drawing’s datum so the coordinates land in the frame the inspector uses.