What is the measurement called when you measure from the inside wall of a pipe to the opposite inside wall?

• A. Pipe Radius
• B. Wall Thickness
• C. Pipe Diameter
• D. Outer Diameter

Answer: (C)

This measures the distance across the bore from one inner wall to the opposite inner wall. That dimension is the pipe diameter—the size used for flow through the pipe. Radius would be half of that distance, so it isn’t the full across measurement. Wall thickness is the space between the inner and outer walls, not the interior span. Outer diameter is the measurement across the pipe’s exterior, not inside. So the term that matches the interior cross‑section measurement is pipe diameter.