Inside Diameter (ID)

In the tube industry, the Inside Diameter is the measurement of the hollow space inside a pipe or tube.

Why it matters: Flow capacity. For water or gas pipes, a larger ID means more fluid can flow through.

Calculation: ID = Outside Diameter (OD) - 2 x Wall Thickness.

Confusion: Pipe "size" (Nominal Bore) often refers loosely to the ID, whereas tubing is usually measured by OD.