Bolt Circle Calculator
Disclaimer: This calculator provides estimated bolt-circle coordinates for general planning and reference only. Actual machining accuracy may vary with tooling, material, and machine setup. For final dimensions or CNC programming, verify all measurements with a qualified machinist or CNC professional.
What is a Bolt-Circle Calculator?
A bolt‑circle calculator (also called a PCD or “bolt‑hole circle” tool) turns four basic inputs — diameter, hole count, start angle, and direction — into precise X / Y coordinates for every hole. The calculator here also accepts hole diameter (with its own unit) and outputs a live SVG preview, CSV table, and ready‑to‑paste G‑code. Machinists, fabricators, and CNC programmers can copy the results straight into CAD/CAM or machine controllers for a perfectly even pattern every time.
Benefits & Typical Uses
- Saves time – no hand calculations or spreadsheet trig.
- Reduces scrap – coordinates are precise to 3‑5 decimal places.
- Unit‑flexible – bolt circle and hole can be in either mm or inches; the tool converts on the fly.
- Direct CNC output – built‑in G‑code block for fast copy‑and‑paste programming.
- Ideal for flange drilling, rotary tables, wheel‑stud layouts, index plates, fixtures, and any evenly spaced bolt pattern.
- Check pressure calculations for pipe flanges.
How to Use Our Bolt Circle Calculator
- Bolt‑Circle Diameter
Type the diameter and pick mm or inches. Need to back‑solve from two holes?,while for material sizing calculations use board and batten. Open the Chord → Diameter helper, enter the chord length and total hole count, then click Convert. - Number of holes – total holes around the circle.
- Hole Diameter (optional)
Enter the drill size and choose its unit; the preview shows the true hole size and the table converts automatically. - Start Angle – measured clockwise from the 12 o’clock (vertical‑up) reference. Pick Clockwise or Counter‑clockwise for the numbering direction.
- X / Y offsets – move the entire pattern if your machine origin is not at the circle centre.
- Output Below. • The SVG preview redraws. • The table lists Hole, Angle, X, Y, Diameter. • Use Copy as CSV or Show G‑code for instant data export.
- Use the floating Back to Top button to jump back up after scrolling. Hit Reset to return all fields to their defaults.
Input Parameters Explained
Input | What It Means |
Number of holes (N) | How many holes do you want around the circle? |
Bolt circle diameter or radius (D or R) | Size of the invisible circle that the holes follow. |
Starting angle | Angle for placing the first hole, starting from the right side (X-axis). |
Centre coordinates (optional) | X and Y position of the circle’s center, if it is not at (0, 0). |
Units | Choose inches or millimetres. Use the same unit throughout the calculation. |
Step-by-Step Guide
- First, select your preferred units. You can choose millimeters or inches.
- Type the number of holes you want. For example, enter 6 if you want a hexagon.
- After that, enter the bolt circle diameter.
- Set the starting angle. If you enter 0°, the first hole will be on the right. Positive angles move the holes counterclockwise. Negative angles move them clockwise.
- Next, select the number of decimal places.
- After that, select the direction. You can choose clockwise or anticlockwise.
- (Optional) Enter the X and Y coordinates of the circle’s center if it is not (0, 0).
- Click “Calculate.” You will see the X and Y positions for each hole.
- Copy or download the table. You can use this in your CAD or CAM software for drilling or cutting.
Understanding the Output (X, Y Coordinates)
This bolt hole circle calculator returns a table with a row for each hole. A typical output looks like this.
Hole # | X Coordinate | Y Coordinate |
1 | 0 | 50 |
2 | -43.301 | 25 |
3 | -43.301 | -25 |
Downloading or Copying Results
After you calculate the bolt circle, our bolt hole circle calculator will show a table with the X and Y coordinates. You can usually copy this table or download it as a CSV or TXT file. This makes it easy to use the data in CAD, CAM, or spreadsheet software.
What is a bolt circle?
A bolt circle is an imaginary circle used to place bolt holes in a round pattern. These holes are spaced evenly around a center point. You can see this in parts like wheel hubs, flanges, or bicycle chainrings. The bolt holes do not sit randomly. They follow the edge of this imaginary circle.
The size of the circle is called the bolt circle diameter (BCD) or pitch circle diameter (PCD). It is an important measurement. Manufacturers use a bolt pattern to show two things: how many bolt holes there are and how wide the circle is. For example, a pattern labeled 5×100 means there are five bolt holes placed evenly around a circle that is 100 millimeters wide.
Understanding Bolt Circle Layouts
What is Bolt Circle Diameter (BCD)?
Bolt Circle Diameter, or BCD, is the diameter of an imaginary circle that runs through the center of each bolt hole. Engineers use this measurement when designing parts like bicycle chainrings, pipe flanges, or machine components. For example, many 5-bolt bicycle chainrings follow a BCD of 130 mm or 110 mm. Some parts, like triple chainsets on bicycles, use more than one BCD. The outer chainrings might use a larger BCD, while the inner one uses a smaller BCD.
Common Uses of Bolt Hole Patterns
Bolt hole patterns are used in many fields. In cars, the bolt circle helps match the right wheel to the hub. For example, a 5×100 pattern means five bolts placed evenly around a 100 mm circle. Machines, motors, and gearboxes often have bolt patterns with four or more holes to help with stable mounting.
Terminology: PCD vs BCD
PCD (Pitch Circle Diameter) and BCD (Bolt Circle Diameter) mean the same thing.
In car and machine work, people often say PCD. In bicycle or small parts work, people say BCD. They are just two names for the same thing.
Typical Bolt Circle Configurations (3, 4, 5, 6, 8 holes)
Hole Count | Pattern Shape | Common Uses |
3 holes | Triangle with equal sides, 120° apart | Small flanges, camera tripod mounts, and some bicycle chainrings |
4 holes | Square or rectangle, 90° between holes | Light car wheels, pipe flanges, and small gearboxes |
5 holes | Pentagon shape, holes 72° apart | Most car wheels (like 5×114.3 mm), many bicycle chainrings |
6 holes | Hexagon shape, holes 60° apart | Pickup trucks, SUVs (like 6×5.5 inch), heavy-duty flanges |
8 holes | Octagon shape, holes 45° apart | Large trucks, strong machines, and industrial pipe flanges |
How to calculate bolt circles
Bolt Circle Formula
If you know the distance between two side-by-side holes (called the chord length) and how many holes there are, you can calculate the bolt circle diameter (BCD).
BCD = C ÷ sin(180° ÷ n)
- C is the distance between two adjacent holes
- n is the total number of holes
This formula works because the holes form a regular shape around a circle, like a triangle, square, or pentagon. Each hole sits at the edge of an invisible circle.
Required Inputs for Calculation
Parameter | Description |
Diameter (D) | Total diameter of the circle |
Hole Count (N) | Number of holes |
Starting Angle | Angle at which the first hole is placed |
Example: Using the Bolt Circle Calculator
Let’s say you want to drill 5 holes around a 100 mm bolt circle. That means the radius is 50 mm. You want the first hole to be at 0°.
The angle between each hole is:
360° ÷ 5 = 72°
Now we use the formula to find the X and Y positions of each hole. Or simply enter the above values into our bolt circle diameter calculator. You will get the following result.
Hole 1: x = 50 mm, y = 0 mm
Hole 2: x ≈ 15.45 mm, y ≈ 47.55 mm
Hole 3: x ≈ –40.45 mm, y ≈ 29.39 mm
Hole 4: x ≈ –40.45 mm, y ≈ –29.39 mm
Hole 5: x ≈ 15.45 mm, y ≈ –47.55 mm
Advantages of Using a Bolt Circle Calculator
Saves Time and Reduces Human Error
When you need to drill or machine holes in a circle, it is important to place them at the right spots. Doing this by hand takes time and can lead to errors. Our bolt circle calculator does all the math instantly and gives you the correct positions. You do not need to measure angles or draw lines. This saves time and helps prevent misaligned holes or wasted materials.
Ensures Precise Hole Placement
In machines or metal parts, holes must be in the right place. If they are off, the part may not fit or could break. Our bolt hole calculator uses exact math to give you the right spot for each hole. You can set the center and angle of the first hole so your pattern matches your design.
Great for CAD/CAM Preparations
If you are using design software or a CNC machine, you need accurate hole locations. Our bolt circle calculator gives you a table of X and Y positions. You can copy these into your design file or G-code.
Supports Multiple Layouts and Patterns
You can use our bolt pattern calculator for any number of holes or any circle size. It works for small parts like a 3-hole flange, car wheels with 5 holes, or large 8-hole machines. This makes the bolt hole calculator helpful for many jobs, like building cars, fixing machines, working with wood or metal, or even building racing game wheels.
FAQs
To find the position of each hole, use these formulas:
x = x₀ + R × cos(A + (i − 1) × 360° ⁄ N)
y = y₀ + R × sin(A + (i − 1) × 360° ⁄ N)
Here:
- x₀, y₀ = center of the circle
- R = radius
- A = starting angle
- i = hole number
- N = total number of holes
This formula gives the exact location of each hole around the circle.
Yes, you can use it for any bolt pattern. Just enter the number of holes, such as 5 for 5-lug or 6 for 6-lug. Our bolt circle diameter calculator spaces them evenly around the circle.
Yes, this can be used for CNC drill setup files. You can copy the coordinates or download them as a CSV or TXT file. These files can go directly into your CAD or CAM software.
The starting angle sets where the first hole goes. A 0° angle places the first hole to the right (along the X-axis). Positive angles turn counterclockwise, and negative angles turn clockwise.
You can choose inches or millimetres. Make sure to use only one unit type for all inputs. Do not mix units, or the results may be wrong.
Yes, our bolt circle diameter calculator shows a simple drawing of the bolt circle and hole positions. This helps you check the layout before drilling.
First, find the radius and number of holes. Then use the following formula.
x = x₀ + R × cos(angle)
y = y₀ + R × sin(angle)
Each hole gets its angle based on its position in the circle. You calculate this for every hole to get the full layout.
You can join parts using bolts, screws, rivets, or welding. If you are using bolts, make sure the bolt holes line up correctly.
After calculating, download or copy the coordinate list. Paste the points into your CAM or G-code software. Make sure the units and origin match your machine setup. You can also adjust decimal places if needed.