Ductile iron pipe measurement methods commonly used require finding the right tools, such as rulers and calipers, to measure the outer diameter, inner diameter, length, and wall thickness of the pipes and pipe fittings. Measure each one individually. The outer diameter of the ductile iron pipe is measured by wrapping around the circumference of the pipe. A caliper is used to measure the inner diameter, and a ruler or tape measure is used for the length. The wall thickness of the ductile iron pipe can be directly measured or indirectly with suitable tools. Industry professionals often estimate the pipe specifications by eye based on their experience.