Bolt Circle Calculator (PCD)
X and Y coordinates of each hole from the pitch circle diameter and number of holes
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Calculates the X and Y coordinates of each hole in an evenly spaced bolt pattern from the pitch circle diameter (PCD), the number of holes and the start angle. Use it to machine or draw flange holes, or to find a PCD from a measured distance.
How to use
- Choose the "Unit" and "Size given as", then enter the "Size" and "Number of holes".
- Set the "Start angle", "0° reference", "Angle direction", "Centre X0" and "Centre Y0".
- For holes on part of the circle, choose "Within an angle" under "Pattern"; list missing holes in "Holes to skip".
- Check the "Hole coordinates" table and drawing, then use "Copy table" or "Save as CSV". A "Hole diameter (optional)" adds the wall between holes.
How it works
- Hole i is at start angle + (i − 1) × 360° ÷ N, with X = X0 + R·cos φ and Y = Y0 + R·sin φ, where R = PCD ÷ 2.
- Neighbouring holes are PCD × sin(180° ÷ N) apart; the wall is this minus the hole diameter. Overlap, or a wall under 10% of the hole diameter, gives a warning.
- "PCD from a measured distance" uses PCD = distance ÷ sin(180° × k ÷ N), where k is the number of holes apart.
Questions and answers
- What are the coordinates for 6 holes on a 100 mm PCD?
- Radius 50, holes 60° apart. From 3 o'clock counterclockwise: hole 1 (50, 0), hole 2 (25, 43.301), hole 3 (−25, 43.301). Neighbouring holes are 50 apart.
- How do I measure the PCD with an odd number of holes?
- No hole is opposite another, so measure between two neighbouring hole centres and enter it under "PCD from a measured distance".
- What does 5×114.3 mean on a car wheel?
- Five bolt holes on a 114.3 mm circle. Neighbouring stud centres are about 67.2 mm apart.
- Can I get the coordinates in clockwise order?
- Set "Angle direction" to "Clockwise". To start from 12 o'clock, choose "12 o'clock" under "0° reference".