NB (Nominal Bore)

In detail

Nominal Bore (NB) or Nominal Pipe Size (NPS) is a dimensionless designator indicating the approximate internal diameter of a pipe in inches. It is not the actual measured dimension but a standardized designation used for pipe selection and compatibility. For example, a 2" NB pipe has an approximate internal diameter of around 50 mm, though the exact dimension varies by schedule (wall thickness). NB is the traditional Indian convention while NPS is the American equivalent.

Where you'll meet this in procurement

You will meet NB (Nominal Bore) on size charts, mill quotes, and fitment checks. Cross-check NB (Nominal Bore) against OD, wall thickness or schedule, length, and end finish so the delivered pipe matches flanges, fittings, and pressure duty—not just a familiar nominal label.

Related terms

• OD (Outside Diameter)The measured external diameter of a pipe in millimeters or inches, critical for fitment.
• Schedule (Sch 40 / Sch 80)Wall thickness designation indicating pressure rating and pipe strength classes.
• Wall Thickness (WT)The radial thickness of pipe material determining strength, weight, and pressure capacity.
• IS 1239BIS standard governing mild steel tubes for water, gas and sewage applications in India.

Related resources

• Pipe schedule chart
• Steel pipe weight calculator
• Request a quotation (RFQ)
• Back to full glossary