Bolt Circle Calculator
Bolt Circle Calculator
To calculate Bolt Circle diameter, input Bolt Circle Diameter and Number of Holes. Select your units (inches or millimeters). The calculator provides X and Y Coordinates for each hole, Angular Spacing, and Center-to-Center distances.
For Equal Spacing, holes are calculated starting from 0° (positive X-axis) going counterclockwise.
How to Calculate Bolt Circle?
To calculate a Bolt Circle diameter, use trigonometric functions to measure hole positions around a circle. Start at the reference angle (typically 0°), then divide 360° by the number of holes to get the Angular Spacing.
For each hole, use sine and cosine functions with the bolt circle radius to find X and Y coordinates. The first hole typically starts at 0° (3 o’clock position) and proceeds counterclockwise.
Bolt Circle Formula
Hole Position Coordinates:
X = (D/2) × cos(θ)
Y = (D/2) × sin(θ)
where:
D = Bolt Circle Diameter
θ = Angle in radians
Angular Spacing:
Angle = 360° ÷ Number of Holes
where:
Angle = Angular separation between holes
Center-to-Center Distance:
C-C = D × sin(180° ÷ Number of Holes)
where:
D = Bolt Circle Diameter
Example 1: Standard 4-Hole Pattern
- Bolt Circle Diameter = 4.00 inches
- Number of Holes = 4
- Angular Spacing = 90 degrees
- Coordinates: (2,0), (0,2), (-2,0), (0,-2)
- Center-to-Center = 2.828 inches
Example 2: 6-Hole Flange
- Bolt Circle Diameter = 120 mm
- Number of Holes = 6
- Angular Spacing = 60 degrees
- Coordinates: (60,0), (30,52), (-30,52), (-60,0), (-30,-52), (30,-52)
- Center-to-Center = 60 mm
Example 3: 8-Hole Pattern
- Bolt Circle Diameter = 6.00 inches
- Number of Holes = 8
- Angular Spacing = 45 degrees
- Coordinates: (3,0), (2.12,2.12), (0,3), (-2.12,2.12), (-3,0), (-2.12,-2.12), (0,-3), (2.12,-2.12)
- Center-to-Center = 2.298 inches
Example 4: Large Flange
- Bolt Circle Diameter = 200 mm
- Number of Holes = 12
- Angular Spacing = 30 degrees
- Coordinates: Listed at 30° intervals
- Center-to-Center = 51.764 mm
Example 5: Small Pattern
- Bolt Circle Diameter = 2.50 inches
- Number of Holes = 3
- Angular Spacing = 120 degrees
- Coordinates: (1.25,0), (-0.625,1.083), (-0.625,-1.083)
- Center-to-Center = 2.165 inches
What is Bolt Circle?
A Bolt Circle (or Bolt Circle Diameter – BCD) is diameter of an imaginary circle passing through the centers of equally spaced holes or bolts in a circular pattern. This measurement is crucial for Flange Design, Wheel Mounting, and other mechanical connections requiring circular bolt patterns. The Bolt Circle dimension, combined with the Number of Holes, determines the exact positioning of holes for proper alignment and mounting.