Construction

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Bolt Circle Calculator.

Calculate regular bolt-circle spacing and coordinates.

On-device calculationNo signup
01

Set your values

Results update as you type.

Radius: 5

Radius

5.000
Circumference: 31.416

Circumference

31.416
Spacing angle: 90

Spacing angle

90.000
Chord spacing: 7.071

Chord spacing

7.071

Use Cases

Machining and fabrication

Quickly determine bolt hole positions for flanges, wheels, or plates without manual trigonometry.

Example: A 10-inch flange with 8 bolts starting at 15°.

Design and CAD modeling

Generate accurate coordinates for creating circular bolt patterns in CAD software or for CNC programming.

Example: Place 6 holes on a 200 mm circle starting at 30°.

Frequently Asked Questions

What is a bolt circle?
A bolt circle is an imaginary circle that passes through the centers of bolts arranged in a circular pattern. The calculator determines the angular spacing and coordinates of each bolt based on the circle diameter, bolt count, and start angle.
How is the start angle used?
The start angle sets the position of the first bolt relative to the horizontal axis (0°). The calculator places the first bolt at that angle and then spaces the remaining bolts evenly around the circle, each separated by 360° divided by the bolt count.
What units does the calculator use?
The circle diameter is entered in any unit (e.g., inches, millimeters). The coordinates are output in the same unit. The start angle is in degrees.

Tips & Common Mistakes

Tips

  • Ensure the bolt count is at least 2 to form a valid circle pattern.
  • Use a start angle of 0° to align the first bolt horizontally to the right.
  • Double-check that your circle diameter is the distance across the center, not the radius.
  • For symmetrical patterns, the start angle can be adjusted to align with existing features.

Common Mistakes to Avoid

  • Entering the radius instead of the diameter, which halves the actual bolt circle size.
  • Forgetting to convert units consistently, leading to incorrect coordinates.
  • Assuming the start angle is measured from the vertical axis when it is from the horizontal.

Last updated: August 13, 2026