Pipe schedule refers to a standardized form of measurement for the sizes of certain types of pipes. It is used for measuring types of pipe that are usually used in industrial applications.
The schedule numbers are assigned to fixed outer and inner diameters for pipes. A schedule number, therefore, demonstrates the thickness of a pipe's walls, instead of other dimensions related to the pipe.
Pipes are used to transport fluids, so an important measurement is their thickness, which demonstrates their capability to carry fluids of certain volumes and pressures, depending on the material of the pipe.
Pressure and schedule
Pipe schedule formerly was used to demonstrate the pressure capacity of a particular pipe, but it no longer has that function because the schedule number is strictly about the dimensions of a pipe and does not take into consideration the material from which it is made. A pipe's pressure capabilities differ with different materials.