When measuring a flange where it’s difficult to directly measure the Pitch Circle Diameter (PCD), you can still calculate it using the measurements of two adjacent holes.

Based on the number of holes on the flange, you can multiply the distance between the holes by a specific factor to estimate the PCD. Here are the factors for different numbers of holes:

For 4 holes: Multiply the distance between two adjacent holes by 1.414.

For 8 holes: Multiply it by 2.613.

For 12 holes: Multiply it by 3.864.

For 16 holes: Multiply it by 5.126.

Example

This 150mm flange has 8 holes and measures 90mm between holes.
PCD = 90 x 2.613 = 235mm

Our flange identification chart suggests this flange is Table D or Table E