How To Measure Pipe Length. The thickness of the pipe wall will vary depending on the pipe, so always take that into account. You can then easily figure the pipe length using one of these methods:
In most industrial applications (such as water or general purpose) the oal is not critical, but in many hydraulic applications the oal can be critical due to space restrictions. Then measure the distance from the surface of the wall to the back of the threaded elbow inside the wall. The close length is 1 1/2, so the remaining unthreaded portion must be 3 1/2.
Use a ruler or tape measure to measure the inner diameter of the pipe.
The dimensional measurement of pipes is crucial for manufacturing to strict tolerances. Measure the outside diameter (od) of your pipe or pipe fitting: Hold the pipe in 1 hand and take a ruler or tape measure in your other hand. Use a ruler or tape measure to measure the inner diameter of the pipe.