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Bolt Circle Calculator

Construction

Find the chord distance between adjacent bolts on a bolt circle pattern. Enter circle diameter and bolt count to get exact spacing and angle between bolts.

Reviewed by the thecalcu.com team · Last updated July 19, 2026

0.560
336

Chord Distance Between Bolts

3
Angle Between Bolts
60

This calculator computes your Chord Distance Between Bolts, Angle Between Bolts from the values you enter.

Inputs
Bolt Circle DiameterNumber of Bolts
Outputs
Chord Distance Between BoltsAngle Between Bolts

What is a Bolt Circle?

A Bolt Circle Calculator finds the chord distance, the straight-line spacing, between adjacent bolts arranged evenly around a bolt circle, based on the circle's diameter and the number of bolts. It also returns the angle between each bolt around the circle.

Bolt circles appear throughout mechanical and structural design: wheel hubs, engine flanges, pipe flanges, mounting plates, and custom fabricated parts all rely on evenly spaced bolt patterns defined by a circle diameter and bolt count.

Why Use a Bolt Circle Calculator?

Laying out a bolt circle by trial and error with a compass and protractor is slow and prone to small errors that compound into misaligned holes. This calculator gives you the exact chord distance to mark with calipers or a ruler, making layout fast and precise for drilling or verification.

It's also useful for cross-checking an existing bolt pattern, if you measure the chord distance between two adjacent bolts on a wheel or flange, you can compare it against the calculator's output to confirm the bolt circle diameter and bolt count match spec.

Who Should Use This Calculator?

Machinists and fabricators use this calculator to lay out custom flanges and mounting plates with precise, evenly spaced bolt holes. Automotive technicians use it to verify wheel bolt patterns before ordering replacement wheels or adapters. Mechanical and structural engineers use it when designing bolted connections that require even load distribution around a circular pattern. Pipefitters and industrial maintenance crews use it to confirm flange bolt spacing matches piping standards. DIYers and hobbyist metalworkers use it for custom project fabrication involving circular bolt patterns.

What Insights Does the Bolt Circle Calculator Give You?

The Chord Distance Between Bolts is the primary result, the straight-line distance you'd measure with calipers or a ruler between the centers of two adjacent bolt holes. This is the number you use directly for marking and drilling. The Angle Between Bolts shows how many degrees separate each bolt position around the full 360-degree circle, useful for setting up a rotary table, indexing head, or angle-based layout tool when drilling the pattern.

How to use this Bolt Circle calculator

  1. Enter the Bolt Circle Diameter in inches, the diameter of the circle passing through the center of each bolt hole.
  2. Enter the Number of Bolts to be evenly spaced around that circle.
  3. Review the Chord Distance Between Bolts result for the straight-line spacing to mark between adjacent holes.
  4. Review the Angle Between Bolts result if you're using an indexing tool or rotary table for layout.
  5. Mark and drill the bolt pattern using the chord distance and angle as your layout reference.
Show formula & methodology ↓Show less ↑

Formula & Methodology

The calculator uses circle geometry to find the chord length between two points on a circle separated by an even angular spacing:

Angle Between Bolts = 360° ÷ Number of Bolts

Chord Distance = Circle Diameter × sin(π ÷ Number of Bolts)

Worked example: For a 6-inch bolt circle diameter with 6 bolts:

Angle Between Bolts = 360° ÷ 6 = 60°

Chord Distance = 6 × sin(180° ÷ 6) = 6 × sin(30°) = 6 × 0.5 = 3.0 in

This means on a 6-inch bolt circle with 6 evenly spaced bolts, each pair of adjacent bolts is separated by exactly 3.0 inches, center to center, with 60 degrees of arc between them.

Frequently Asked Questions

What is a bolt circle?
A bolt circle is an imaginary circle that passes through the center of each bolt hole in a pattern of evenly spaced bolts, commonly found on wheels, flanges, engine blocks, and mounting plates. The bolt circle diameter (BCD) is the diameter of that circle, and it's a critical measurement for matching wheels, hubs, and flanges to the correct bolt pattern.
How do I measure a bolt circle diameter?
For an even number of bolts, measure the center-to-center distance between two bolts directly across from each other on the circle. For an odd number of bolts, measure from the center of one bolt hole to the outer edge of the bolt hole directly across, then verify with a bolt circle gauge or by calculating from three bolt hole positions.
What is the chord distance between bolts?
The chord distance is the straight-line distance between the centers of two adjacent bolt holes on the bolt circle, as opposed to the curved distance along the circle's edge. This is the measurement most commonly used when laying out or verifying a bolt pattern with a ruler or calipers.
Why do wheels have different bolt patterns?
Bolt patterns vary by vehicle manufacturer, wheel size, and load rating, which is why wheels and hubs must be matched by both the number of bolts and the bolt circle diameter, a mismatch in either the bolt count or spacing means the wheel simply won't fit the hub.
How is the angle between bolts calculated?
The angle between adjacent bolts on a bolt circle is simply 360 degrees divided by the number of bolts, since the bolts are evenly distributed around the full circle. For example, a 5-bolt pattern has 72 degrees between each bolt, while an 8-bolt pattern has 45 degrees between each bolt.
Can this calculator help with custom flange or plate fabrication?
Yes, machinists and fabricators use this calculator to lay out evenly spaced bolt holes on custom flanges, mounting plates, and pipe fittings by entering the desired circle diameter and bolt count to get the exact chord spacing needed for drilling.
Does this calculator work for both metric and imperial measurements?
This calculator uses inches for the bolt circle diameter and chord distance, but the underlying trigonometric formula works the same regardless of unit, if you're working in millimeters, simply enter your circle diameter in millimeters and interpret the chord distance result in the same unit.
What's a common bolt pattern for passenger vehicle wheels?
Many passenger cars use a 5-bolt pattern (5 lug nuts), commonly labeled as something like 5x114.3mm, meaning 5 bolts on a 114.3mm bolt circle diameter, always confirm your specific vehicle's bolt pattern before ordering wheels, since it varies significantly by make and model.
How many bolts are typically used in industrial flange connections?
Industrial pipe flanges commonly use 4, 8, 12, or 16 bolts depending on pipe diameter and pressure rating, following standards like ANSI/ASME B16.5, with larger and higher-pressure flanges using more bolts distributed evenly around the bolt circle.
What happens if I drill a bolt circle with the wrong chord spacing?
If the chord spacing is off, the bolt holes won't align evenly around the circle, which can cause uneven load distribution, difficulty threading bolts, or a component that simply doesn't mate correctly with its mating flange or hub, accurate chord spacing calculation before drilling prevents costly rework.
Is the chord distance the same as the arc length between bolts?
No, the chord distance is the straight-line distance between two adjacent bolt centers, while the arc length is the curved distance measured along the circle itself between those same two points, the chord distance is always slightly shorter than the arc length, and it's the chord distance that's used for practical layout with a ruler.
Also known as
bolt pattern calculatorbolt spacing calculatorbolt hole circle calculatorwheel bolt circle calculatorflange bolt circle calculator