Bolt Circle Calculator
ConstructionFind 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.
Chord Distance Between Bolts
3
Angle Between Bolts
60
What is a Bolt Circle?
A Bolt Circle Calculator finds the chord distance โ the straight-line spacing โ 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.
How to use this Bolt Circle calculator
- Enter the Bolt Circle Diameter in inches โ the diameter of the circle passing through the center of each bolt hole.
- Enter the Number of Bolts to be evenly spaced around that circle.
- Review the Chord Distance Between Bolts result for the straight-line spacing to mark between adjacent holes.
- Review the Angle Between Bolts result if you're using an indexing tool or rotary table for layout.
- Mark and drill the bolt pattern using the chord distance and angle as your layout reference.
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 = 360ยฐ รท Number of Bolts Chord Distance = Circle Diameter ร sin(ฯ รท Number of Bolts) Worked example: For a 6-inch bolt circle diameter with 6 bolts: Angle Between Bolts = 360ยฐ รท 6 = 60ยฐ Chord Distance = 6 ร sin(180ยฐ รท 6) = 6 ร sin(30ยฐ) = 6 ร 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
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.
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.
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.
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 โ a mismatch in either the bolt count or spacing means the wheel simply won't fit the hub.
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.
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.
This calculator uses inches for the bolt circle diameter and chord distance, but the underlying trigonometric formula works the same regardless of unit โ if you're working in millimeters, simply enter your circle diameter in millimeters and interpret the chord distance result in the same unit.
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 โ always confirm your specific vehicle's bolt pattern before ordering wheels, since it varies significantly by make and model.
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.
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 โ accurate chord spacing calculation before drilling prevents costly rework.
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 โ 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