In the intricate world of engineering and industrial applications, accurate measurements are paramount. When it comes to flange installations, precision is the key to ensuring a seamless fit and optimal performance. In this comprehensive guide, we delve into the nuances of how to measure flange size and flange PCD (Pitch Circle Diameter), providing you with essential insights and techniques.

Understanding Flange Size and Flange PCD

Flanges are vital components in pipelines and machinery, connecting pipes, valves, and other equipment securely. Flange size refers to the diameter of the flange, while the Pitch Circle Diameter (PCD) signifies the circle passing through the centre of all bolt holes. Proper measurement of these aspects is crucial for the successful assembly of flanged connections.

How to Measure Flange Size

  • Gather your tools: To measure flange size, you will need a calliper, a tape measure, a pencil and a paper to record your measurement.

gather your tools

  • Diameter Measurement:  To measure flange size accurately, start by determining the diameter. Use a calliper, ensuring it is placed perpendicular to the pipe or equipment surface. Record the measurement precisely, taking care to avoid any deformities or irregularities.

Diameter Measurement

  • Bolt Hole Count: Count the number of bolt holes present on the flange. Standard flanges typically have four, six, or eight holes, but the count can vary based on the flange type and size. Make sure to include this information in your measurements.

Bolt Hole Count

  • Bolt Hole Diameter: Measure the diameter of a single bolt hole using a micrometer or calliper. Multiply this value by the total number of bolt holes to calculate the PCD accurately.

Bolt Hole Diameter

How to Measure Flange PCD

  • Determining the Bolt Circle: Place a ruler or tape measure at the centre of one bolt hole and extend it to the centre of the opposite bolt hole. The measurement you get represents the bolt circle diameter or PCD.

Determining the Bolt Circle

  • Calculating PCD: For flanges with an even number of bolt holes, measuring directly across from one bolt hole to its opposite provides the PCD. For flanges with an odd number of bolt holes, measure from the centre of any bolt hole to the space between the two opposite bolt holes.

calculate flange PCD

  • Record Measurement: write all the measurement on a paper.

record measurement

Simplified size chart for standard flange sizes and their associated PCD measurements:

Flange Size (Nominal Diameter)

Pitch Circle Diameter (PCD)

1/2 inch (15 mm) 95 mm
3/4 inch (20 mm) 105mm 
1 inch (25 mm)  115mm
1 1/4 inch (32 mm) 140mm
1 1/2 inch (40 mm) 150mm
2 inch (50 mm)  165mm
2 1/2 inch (65 mm)  185mm
3 inch (80 mm)  200mm
4 inch (100 mm) 220mm
5 inch (125 mm) 250mm
6 inch (150 mm) 285mm
8 inch (200 mm) 340mm
10 inch (250 mm) 395mm
12 inch (300 mm) 445mm
14 inch (350 mm) 505mm
16 inch (400 mm) 565mm
18 inch (450 mm)  615mm
20 inch (500 mm)  670mm


Mastering the art in measure flange size and flange PCD is indispensable for engineers, technicians, and anyone involved in industrial applications. By following the methods outlined in this guide, you can achieve precision in your measurements, leading to robust, leak-free flange connections. Incorporating these accurate measurements into your projects will not only enhance the structural integrity of your systems but also contribute significantly to the overall safety and efficiency of your operations. So, the next time you embark on a flange installation project, remember the importance of precise measurements, and your industrial endeavours will undoubtedly reap the benefits of your meticulous approach.

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Frequently Asked Questions about Measuring Flange Size and Flange PCD

Why is it essential to measure flange size accurately?

Accurate measurement of flange size ensures a perfect fit between mating flanges, preventing leaks and ensuring the structural integrity of the joint. Proper measurements also facilitate the selection of compatible gaskets, bolts, and nuts, crucial for the overall effectiveness of the connection.

Can I use a regular ruler to measure flange PCD?

While a regular ruler can give you an approximate measurement, it is advisable to use a dedicated measuring tool, such as a calliper or tape measure, for precise results. These tools provide accurate readings, especially when dealing with critical industrial applications.

What is the significance of flange PCD in the installation process?

Flange PCD (Pitch Circle Diameter) is vital as it determines the arrangement of bolt holes on the flange. Proper measurement of PCD ensures that bolts are evenly distributed, promoting uniform pressure and a secure connection. This uniformity is essential for preventing leaks and maintaining the integrity of the joint over time.

Are there standard measurements for flange size and PCD?

Flange size and PCD measurements can vary based on industry standards and specific applications. It is crucial to refer to relevant standards (such as ASME, DIN, or JIS) and specifications provided by manufacturers. These standards outline the dimensions and tolerances necessary for various types of flanges, ensuring compatibility and reliability in industrial settings.

What precautions should I take while I measure flange size and PCD?

When measuring flange size and PCD, ensure that the measuring tools are clean and well-maintained to obtain accurate readings. Additionally, be mindful of any irregularities, deformities, or damages on the flange surface, as these can affect measurements. Double-check your measurements and consider seeking assistance from experienced professionals if you are unsure about the accuracy of your readings.

Can I use the same gasket for flanges with different sizes but similar PCD?

It is not recommended to use the same gasket for flanges with different sizes, even if they have similar PCD. Each gasket is designed to match specific flange dimensions. Using an incorrect gasket can compromise the seal, leading to leaks and potential system failures. Always choose gaskets that are compatible with the specific flange size and material you are working with.

How I often measure flange size and PCD in industrial equipment?

Flange size and PCD should be measured whenever a new installation is being carried out or when replacing existing flanges. Regular inspections and measurements are also advisable during scheduled maintenance checks to ensure the continued integrity of the connections. Keeping a proactive approach to measurements helps prevent issues and ensures the smooth operation of industrial equipment

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