How is the diameter of commercial pipe typically measured?

The diameter of commercial pipe is typically measured using the nominal pipe size. This sizing system does not correspond directly with the actual outside or inside diameter of the pipe, instead providing a standardized designation that simplifies communication regarding pipe dimensions across many applications.

Nominal sizes are used because they offer a practical and widely accepted reference, making it easier for engineers, contractors, and tradespeople to identify and select compatible piping for construction and repair. For instance, a pipe labeled as 2 inches nominal may actually have specific outside and inside diameters that differ from that measurement, yet everyone understands the reference to "2-inch" nominal size in the context of application.

This method of sizing is significant for compatibility with fittings and other components that are designed to align with these standardized nominal measurements, ensuring a reliable connection. Other measurement methods, such as actual measurements or material thickness, do not provide this same standardization and ease of identification for practical applications in the field.