⚙️ Bolt Circle Calculator
📍 Hole Coordinates (relative to center)
| Hole # | Angle (°) | X | Y |
|---|
How to Use the Bolt Circle Calculator
Our bolt circle calculator is designed for engineers, machinists, and DIY enthusiasts who need precise hole patterns for flanges, wheels, gears, or any circular arrangement. Enter the circle diameter, number of holes, and starting angle — the calculator instantly provides angular spacing and XY coordinates for drilling or CAD work.
Understanding Bolt Circles
A bolt circle (or pitch circle) is the imaginary circle that passes through the centers of equally spaced holes. Common applications include:
- Wheel lug patterns (e.g., 5×114.3mm).
- Pipe flanges in plumbing and industrial piping.
- Gear and sprocket mounting.
- Machined parts with multiple fasteners.
Formulas Used
The calculator uses basic trigonometry. For N holes equally spaced:
- Angular spacing = 360° / N.
- Hole angle = start angle + (i-1) × spacing (with direction considered).
- Coordinates: X = R × cos(θ), Y = R × sin(θ), where R = D/2.
All angles are in degrees, and coordinates are relative to the circle center. You can switch between mm and inches.
🔧 Example from reference (typical): A 6-bolt flange with diameter 100 mm. Holes at 0°, 60°, 120°, 180°, 240°, 300°. Coordinates: (50,0), (25,43.3), (-25,43.3), (-50,0), (-25,-43.3), (25,-43.3) mm. Perfect for drilling!
Why Accurate Bolt Circles Matter
In precision engineering, even small angular errors can cause misalignment, vibration, or part failure. This bolt circle calculator eliminates guesswork, giving you reliable numbers for:
- CNC programming and manual machining.
- Checking existing patterns (enter your measured diameter and count).
- Designing custom flanges or adapters.
Frequently Asked Questions
Can I use this for odd numbers of holes?
Absolutely. It works for any N ≥ 2. For N=3, you’ll get a triangle; for N=5, a pentagon, etc. The diagram updates to show the pattern.
What’s the difference between clockwise and counter-clockwise numbering?
It simply changes the order of holes in the table and the angle progression. Physically, the holes remain at the same positions; the numbering helps if your drawing specifies a particular sequence.
How do I measure the bolt circle diameter?
For an even number of holes, measure from the center of one hole to the center of the opposite hole. For odd numbers, you can measure from a hole to the edge of the center hub, or use specialized formulas. Our calculator assumes you already know D.
Can I get coordinates for drilling on a lathe or mill?
Yes — the X and Y values are cartesian coordinates from the center. For a mill, you can move to each (X,Y). For a lathe with a milling attachment, you’d typically use the angular positions.
Bookmark this bolt circle calculator for quick reference in the workshop. At SmartUnitCalculator.com, we’re building tools that turn complex geometry into simple numbers.