The 'C' factor of a water pipe is the measurement of the ___ of a pipe.

• A. interior roughness
• B. diameter
• C. wall thickness
• D. length

Answer: (D)

C factor is a roughness coefficient that describes the interior surface of the pipe. It measures how smooth or rough the wetted inside surface is, which directly affects friction losses as water flows. A smoother interior allows water to move with less friction, giving a higher C value; a rougher inside surface increases friction and lowers the C value. This factor is used in flow equations to account for the pipe’s material and condition, not for its physical size or length. Diameter and length influence how much water can flow and how much head loss accumulates, while wall thickness relates to strength and may affect roughness if corrosion or deposits are present, but the standard C factor itself specifically targets interior roughness.