Imperial Si Metric Pipe Sizes

Overview

Engineering reference data for Imperial Si Metric Pipe Sizes in piping systems.

Key Formulas

Continuity

$A_1 v_1 = A_2 v_2$

Mass conservation in pipe flow.

Pressure Drop

$\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}$

Darcy-Weisbach equation.

Pipe Area

$A = \frac{\pi D^2}{4}$

Cross-sectional area of a pipe.

Variables

Symbol	Description	Unit
$D$	Pipe diameter	m
$v$	Flow velocity	m/s
$\Delta P$	Pressure drop	Pa
$f$	Friction factor	—

Imperial to Metric Pipe Size Conversion Table

The following table provides a comprehensive comparison between nominal imperial pipe sizes (NPS) and nominal metric pipe sizes (DN), along with common standards from major organizations. These conversions are essential for international projects and material procurement.

Understanding Pipe Sizing Systems

The United States is the only major industrial country that predominantly uses the imperial (inch-based) Nominal Pipe Size (NPS) system. The rest of the world primarily uses the metric Nominal Diameter (DN) system.

It is critical to understand that nominal sizes are not the actual physical dimensions of the pipe. For instance:

• A 1-inch NPS pipe has an outside diameter (OD) of 1.315 inches (33.4 mm), not 1 inch.
• The DN number roughly corresponds to the internal diameter of the pipe in millimeters for smaller sizes, but this relationship becomes approximate for larger pipes.

The table includes dimensions from several key standards bodies:

• ASHRAE & AWWA: Common in HVAC and water/wastewater applications in North America.
• NFPA: Sizes used in fire protection systems.
• ASTM Copper Tube: Specific dimensions for copper tubing used in plumbing and refrigeration.

Note: A "-" indicates that the specific dimension is not commonly defined or used for that size under that standard.

Interactive Charts

References

• Original Source