Pipe Diameter Conversion Table

Nominal Pipe Size (NPS)

In the industrial market of the United States, a measurement system called Nominal Pipe Size (NPS) is widely used.

NPS is defined by the American standard ANSI/ASME and is based on inches, representing the approximate outside diameter of a pipe. NPS values are often expressed as fractions or decimals (for example, 2 1/2″ or 2.5 inches).

NPS is primarily used in the United States and serves as a standard for determining pipe size in various industries. American standards provide guidelines for the manufacturing, design, and maintenance of piping systems to ensure consistency and uniformity in the industry.

Nominal Diameter (DN)

In the industrial market of Europe, a measurement system known as Nominal Diameter (DN) is typically used.

DN is defined by the European standard ISO 6708 and is based on millimeters, representing the approximate internal diameter of a pipe. DN values are usually expressed as whole numbers (for example, DN50).

DN is widely used as the standard measurement system for pipes and related components in many countries outside the United States. European standards provide specifications for various aspects of piping systems, including dimensions, materials, and testing methods. These standards ensure compatibility between different manufacturers and facilitate international trade.

DN, in another definition, is the imprecise conversion of NPS units to metric units. The DN conversion system simplifies by ignoring the decimal point and rounding to the nearest zero or five.

For example:

• 1 inch equals 25.4 millimeters but is presented as DN25.
• 8 inches equals 203.2 millimeters but is presented as DN200.
• A 14-inch flange is called DN350.

Below is a conversion table from NPS to DN: