PIPE CHART INSIDE DIMENSIONS (ID)

COMPLETE PIPE SPECIFICATIONS REFERENCE

This comprehensive chart provides critical dimensions and pipe sizes from 1/8" to 30". Use this reference to select the right pipe specifications for your project, ensuring compatibility with our paddle blinds, blind flanges, and isolation solutions by finding your nominal pipe size, then select the appropriate schedule designation based on your project requirements. This chart is perfect for engineers, operators, project managers, and suppliers to determine the flow rate and structural pipe system design.

WHY DO PIPE ID AND SCHEDULE GET MISTAKEN?

Pipe ID (Inside Diameter) and Schedule are two separate dimensions that get tangled because they’re interdependent and both affect wall thickness — but in different ways.

Here’s the core of the confusion, broken down:

1. NPS is not the actual ID. “Nominal Pipe Size” is a historical trade designation — NPS 3 pipe has an OD of 3.5″, not 3″. The nominal number is essentially meaningless as a real measurement.

2. OD is fixed per NPS; schedule moves only the wall inward. Once you pick NPS 3, every schedule of NPS 3 pipe has the same 3.5″ OD. What changes is the wall thickness. Higher schedule = thicker wall = smaller bore (ID). So people spec “Sch 40” thinking they’re setting the ID, when they’re actually only setting the wall.

3. The cross-NPS trap. Because different NPS pipes have different ODs, a larger NPS pipe at a heavy schedule can end up with nearly the same ID as a smaller NPS pipe at a lighter schedule — even though they look wildly different on paper. This catches people off guard when they’re sizing for flow rather than pressure rating.

4. ID governs flow; schedule governs pressure rating. Engineers focused on pressure rating think in schedule. Engineers focused on flow or instrument connections think in ID. When you hand a drawing across disciplines without being explicit about which parameter you’re specifying, mistakes happen.

A good rule of thumb: Always state both NPS and schedule together (e.g., “NPS 3, Sch 80”), then verify the resulting ID against your flow calculations separately. Never assume specifying one implies the other.

WHEN DOES THE NPS ACTUALLY MATCH THE DIAMETER?

NPS 1/8 to 12: The nominal size matches neither the ID nor the OD exactly.

NPS 14 and Above: The OD matches the nominal size (example: 14-inch pipe has a 14-inch OD).
*The ID still varies based on the wall thickness.