Some common pipe fitting dimensions are 1-, 2-, and 3-inch pipe with varying pipe thicknesses, depending on intended use. The most common pipe for any of these dimensions by far is the schedule 40 size, which accounts for over 30 percent of steel pipe produced in the United States.
Other common pipe thicknesses are schedule 5, schedule 10 and schedule 160 pipe. Pipe schedule is calculated through a formula that takes into account the thickness of the pipe, the internal pressure and the allowable stress that the pipe can take. Due to increased thickness and material cost, the higher the schedule rating, the more costly the pipe.