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How To Measure A Flange

Measuring A Standard Flange

It’s important to get the correct flange. Measure your flange using the guide below and review the measurements of flanges available from The Metal Company to see what corresponds exactly. One of the most important measurements is the Pitch Circle Diameter (PCD) which can determine if the flange bolt holes will match each other.

The PCD is from centre to centre of opposing boltholes. The easiest way to measure this is from the external edge of one hole to the internal edge of the other.

The next measurement you need is the inside diameter, also known as the ID. Here you measure across the centre to identify whether this flange is for tube or pipe and what size it fits.

It can also be helpful to measure the outside diameter although this isn’t as critical. This is measured from one external edge to the other.

Lastly you need to measure the bolt hole size across the hole – this tells us what size bolts we need. Typically you use bolts two millimetres smaller than the bolt hole size. 

It is also important to count the number of bolt-holes and sometimes measuring the thickness of the flange can help make sure you have the correct flange for the application.

Once you have your measurements, check out the chart below which will help with identifying which flange you require.

FLANGE MEASUREMENTS

A: INSIDE DIAMETER
Measure across the centre from one side of the internal hole to the opposite side of the hole.

B: OUTSIDE DIAMETER
Measure across the centre from the external edge to the other external edge of the flange.

C: PITCH CIRCLE DIAMETER (PCD)
Measure from centre of the bolt hole to centre of the opposite bolt hole. This can also be measured from the external edge of the bolt hole to the internal edge of the opposite bolt hole.

D: HOLE SIZE
Measure from edge to edge, across the centre of a bolt hole. This will generally be slightly larger than the metric bolt being used.

E: THICKNESS
Measure from one edge of the flat face to the other.