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Bolt Circle Diameter Calculator

Easily find bolt circle diameter with our free calculator. Enter your values and get instant results. Simple, fast, and accurate.

Minimum 3 holes required
1 = adjacent holes, 2 = skip one hole, etc.
Measure center-to-center distance between bolt holes

Ever tried to measure the distance between holes on a wheel or gear and felt stuck? You’re not alone. That’s why we built the Bolt Circle Diameter Calculator. It’s a handy online tool that helps you get the exact size of a bolt circle without tough math. You’ll save time, avoid errors, and get results in the unit you want.

Think of it like having a skilled machinist in your pocket. You type in the number of holes, the step count, and the distance you measured. The calculator does the math and shows the correct bolt circle diameter in seconds.

What is Bolt Circle Diameter?

Bolt Circle Diameter, or BCD, is the size of the circle that runs through the center of all the holes in a pattern. Mechanics also call it Pitch Circle Diameter (PCD). If you’ve seen car wheels, chainrings on a bike, or industrial flanges, you’ve already seen bolt circles in action.

How to Use the Calculator

Using the calculator is as easy as pie. Just follow these steps:

Step 1: Enter Number of Holes

Put in how many holes are in the circle. It must be three or more.

Step 2: Enter Step Count

Step count is how far apart the two holes are that you measured. For holes side by side, the step count is one.

Step 3: Enter Chord Length

This is the straight line from the center of one hole to the center of another. Make sure you measure it right.

Step 4: Pick Units

You can work in mm, inches, or other units. The tool will convert them for you.

Step 5: Get Results

Hit calculate and see the bolt circle diameter right away. The tool even shows you unit conversions if needed.

The Calculation Formula

Here’s the formula used by the calculator in plain text:

Bolt Circle Diameter = Chord Length ÷ sin(π × Step Count ÷ Number of Holes)

For example, if you have 5 holes, a step count of 1, and a chord length of 64 mm:

Angle = π × 1 ÷ 5 = 36°

sin(36°) = 0.5878

BCD = 64 ÷ 0.5878 = 108.9 mm

Why Use This Calculator?

You don’t need to waste time with charts or guesswork. The Bolt Circle Diameter Calculator is fast, simple, and works for both metric and imperial systems. Whether you’re fixing a car, fitting a bike part, or working on a machine, this tool saves you the headache.

Final Verdict

Measuring bolt circles can feel like a puzzle, but it doesn’t have to. Our calculator makes the job stress-free. Just enter a few numbers and you’ll have the answer in seconds. Clear, quick, and accurate that’s what makes it useful for pros and DIY lovers alike.

FAQs

What is the difference between BCD and PCD?

They mean the same thing. BCD is used more in bikes, while PCD is common in cars.

Can I use this calculator for any unit?

Yes. You can choose mm, inches, feet, and more.

What if I measured wrong?

The calculator will still work, but the result won’t match the real part. Always measure center to center for best results.

Do I need to know advanced math?

Not at all. The tool does the math for you.