SKY-001 / Engineering tools
Bolt Circle Calculator
Calculate equally spaced hole centers from a known pitch circle diameter. Inspect the diagram, copy coordinates or download a CSV in your browser.
Calculations run locally in your browser. Inputs are not sent to Studio, and using this tool requires no account.
Top view: +X points right, +Y points up. Start angle is measured counterclockwise from +X, even when numbering clockwise. Hole 1 is at the start angle. Table angles are normalized to [0°, 360°).
Hole center coordinates
- Pitch circle radius
- 50 mm
- Angular spacing
- 90°
Axes pass through the entered center, not the global origin. Markers denote centers, not hole diameters. Labels are omitted above 32 holes; the table always lists every hole.
| Hole | Angle (°) | X (mm) | Y (mm) |
|---|---|---|---|
| 1 | 0 | 50 | 0 |
| 2 | 90 | 0 | 50 |
| 3 | 180 | -50 | 0 |
| 4 | 270 | 0 | -50 |
Copy this brief, open Studio, then add the missing part dimensions and review the generation cost before submitting. Nothing is submitted automatically.
Open StudioFormula and worked example
For hole i = 0…n−1: R = PCD/2; Δθ = 360°/n; θᵢ = θ₀ ± iΔθ; Xᵢ = Cx + R cos θᵢ; Yᵢ = Cy + R sin θᵢ. Use + for counterclockwise and − for clockwise numbering. Trigonometric calculations convert degrees to radians.
Example: 4 holes on a 100 mm PCD, center (0, 0), start 0°, counterclockwise → (50, 0), (0, 50), (−50, 0), (0, −50) mm; spacing 90°.
PCD is the entered diameter, not inferred from an unknown bolt pattern. This is not G-code, a drilling program, a fit check or a structural calculation. Screen and brief values use up to 10 significant digits; CSV retains numeric precision.
Changing mm/in converts entered dimensions instead of reinterpreting them. 1 in = 25.4 mm exactly. NIST unit conversion tables
Frequently asked questions
Can I enter a negative center or start angle?
Yes. Center X/Y and the start angle are signed; the diameter must stay positive. A −90° start is equivalent to 270°.
Does the calculator determine the hole size?
No. The markers and CSV describe hole centers only. Choose the hole diameter, edge distances and tolerances separately before modeling or machining.
Can I use inches?
Yes. Switching units converts PCD and both center coordinates. Angles and hole count are unchanged. Floating-point rounding may occur.