Geometry and layout calculator
Bolt Circle Calculator
Lay out evenly spaced holes around a bolt circle and list the angle and coordinates for each one.
What the result means
The angle tells you where each hole center falls as you move around the circle. The X and Y values show the location of each hole center from the middle of the bolt circle. That is useful if you are laying the pattern out on a machine, a drawing, or a part that already has a known center.
Formula
Angle between holes = 360° ÷ number of holes
X = radius × cos(angle)
Y = radius × sin(angle)
Worked example
A 5 hole pattern on a 4.5 inch bolt circle has 72° between holes. The radius is 2.25 inches. Starting at 0°, the first hole is at X = 2.25 and Y = 0. The next hole is 72° farther around the circle.
Common mistakes
- Using the outside diameter of the flange instead of the bolt circle diameter.
- Measuring to the edge of a hole instead of the center of the hole.
- Reversing clockwise and counterclockwise directions between a sketch and a machine.
- Forgetting that zero degrees may be defined differently on different machines.
What this calculator cannot check
It can place the pattern, but it cannot tell whether the flange is thick enough, the hole spacing is strong enough, or the fasteners are right for the load.