Center distance between holes is an important layout calculation in drilling, machining, and fixture design. It is used when holes must be placed evenly around a circle or positioned accurately in a pattern.
This formula page explains how the hole spacing is determined, how the pitch circle diameter affects the result, and how to work through a simple example before using the calculator page.
The live calculator is available through the back link below. This page focuses on the formula and practical interpretation.
For holes placed on a circular pattern, the hole centers lie on a pitch circle. The pitch circle diameter tells you the size of the circle on which the holes are arranged.
Once the radius is known, the spacing between adjacent hole centers can be calculated from the angle between the holes.
When holes are evenly spaced around a circle, the center-to-center distance between neighboring holes is the chord length.
Here, R is the pitch circle radius. This formula gives the straight-line center distance between one hole and the next hole in the pattern.
Suppose you need 6 holes on a pitch circle diameter of 120 mm.
Step 1: Find the radius.
120 ÷ 2 = 60 mm
Step 2: Apply the spacing formula.
Hole Spacing = 2 × 60 × sin(180° ÷ 6)
Step 3: Simplify the angle.
Hole Spacing = 120 × sin(30°)
Step 4: Final result.
Hole Spacing = 120 × 0.5 = 60 mm
So the center distance between adjacent holes is 60 mm.
Accurate hole spacing is essential in flange drilling, rotary fixtures, bolt-circle layouts, and machine parts that must assemble correctly. Even a small error can affect fit, alignment, and load distribution.
In workshop work, this calculation helps before drilling begins so the layout marks are placed correctly the first time. It is especially useful when making repeating parts or checking a drawing against an actual component.
| Layout Type | How It Is Measured | Typical Use |
|---|---|---|
| Circular hole pattern | Spacing is based on pitch circle diameter and number of holes. | Flanges, bolt circles, rotary plates |
| Straight hole pattern | Spacing is measured directly along a line or coordinate axis. | Plates, brackets, linear drilling layouts |
What is the center distance between holes?
It is the straight-line distance from the center of one hole to the center of the next hole in a layout.
Why do I need pitch circle diameter?
The pitch circle diameter defines the circle on which the hole centers are placed, so it is required for accurate spacing.
Does the number of holes change the spacing?
Yes. More holes on the same circle means the angle between holes becomes smaller and the center distance changes.
Can this formula be used for flange drilling?
Yes. It is commonly used for flange bolt circles, fixtures, and other circular drilling layouts.