Bolt Circle Calculator
Calculate equally spaced hole centers for a flange, connection plate, or fixture. Choose a start angle and origin, then download the X/Y coordinates.
Pattern inputs
Hole coordinates
- Angular spacing
- 60°
- Adjacent center chord
- 2 in
| Hole | Angle | X (in) | Y (in) |
|---|---|---|---|
| 1 | 0° | 2 | 0 |
| 2 | 60° | 1 | 1.7321 |
| 3 | 120° | -1 | 1.7321 |
| 4 | 180° | -2 | 0 |
| 5 | 240° | -1 | -1.7321 |
| 6 | 300° | 1 | -1.7321 |
Preview is scaled to fit, not a full-size cutting template. CSV keeps unrounded calculation values.
Method
Enter the pitch circle diameter: the diameter through the hole centers, not the outside edge of the plate. The first hole starts at the entered angle. Zero points toward +X and positive angles run counterclockwise, with +Y upward. Center X and Y shift the whole pattern without changing its spacing. The preview follows those axes; use the coordinate table or CSV for numerical values.
Angular spacing = 360° ÷ hole count. For hole i starting at i = 0: θᵢ = start angle + i × spacing. xᵢ = center X + (pitch diameter ÷ 2) × cos(θᵢ). yᵢ = center Y + (pitch diameter ÷ 2) × sin(θᵢ). Adjacent center chord = pitch diameter × sin(π ÷ hole count), for at least two holes.
Worked example
Six holes on a 4 in pitch circle have 60° spacing and a 2 in adjacent center chord. With center (0, 0) and start angle 0°, the first three centers are (2, 0), (1, 1.7321), and (−1, 1.7321) in. Moving the center to (10, 5) adds 10 in to every X and 5 in to every Y.
Limits
This calculates ideal hole-center geometry. It does not choose a bolt size, check plate edge distance, verify a connection load, or add laser kerf or cutter compensation. Overlapping adjacent hole diameters trigger a warning. The preview scales to fit the screen and is not a full-size template; do not measure it with a ruler. CSV coordinates retain the calculation precision instead of the rounded table display.