To read a PVC pipe dimension chart, first identify the pipe schedule, which refers to the thickness of the pipe wall. Choose a nominal pipe thickness, or general size classification, from the far left column. Read to the right to find the pipe specs. The specs appear at the top of each column. PVC pipe dimension carts usually specify the outside diameter, the average inside diameter and the minimum wall thickness.
The outside diameter is the measurement from one outside edge to the opposite outside edge. The average inside diameter is the distance from one inside edge of the pipe to the opposite inside edge.
The minimum wall thickness column notes the thinnest possible pipe wall for the specified size and schedule. Next to this number, the chart may include a tolerance. This number indicates the potential amount of variation from the minimum wall thickness. Tolerance is usually given in a positive decimal number. If a pipe has a tolerance of +.020, it means that the wall may be up to 0.020 inches thicker than the minimal wall thickness.
The nominal pipe thickness is an important number, as it determines the compatible PVC fittings. This measurement is usually given in inches.