At what pipe diameter does measuring by the outside diameter begin?

Measuring by the outside diameter of pipes begins at a diameter of 14 inches. This practice is important because it provides a consistent method of measurement that is necessary for the fabrication and installation of larger pipe systems.

For smaller pipes, measurements are typically taken using the nominal pipe size, which corresponds more closely to the internal diameter. However, as the diameter increases, the differences between the internal and external measurements become significant enough that using the outside diameter offers greater accuracy and clarity in construction specifications and fittings.

Thus, for pipe sizes 14 inches and above, using the outside diameter ensures that all measurements account for the thickness of the pipe walls, which can vary based on material and application. This practice also simplifies the process of matching pipe sections and fittings, ultimately leading to a more efficient installation process.