This is a general guide for people who need to know the actual outer and inner diameters of commonly used ABS, PVC, and CPVC pipes. It can be for figuring out the pipe size if there are no visible markings or determining what size hole needs to be drilled or if something can fit somewhere. There may be some minor variations due to different manufacturers. I've also included information on the allowed slope & trap arm length according to UPC and IPC, but remember to always check your local codes to make sure these rules apply. Some jurisdictions that use IPC restrict the 2" lines to 6' instead of 8'. Just remember that the developed length of the trap arm cannot exceed the nominal pipe diameter. If it does, the vents will not work. I found the information for PVC at Petersen Products. If you click the link, it has additional information such as OD & ID for other pipe sizes as well as wall thickness, pressure tolerance, and temperature tolerance. This site also has information on temperature and pressure tolerances for CPVC, but did mention that CPVC has a different inner diameter than PVC. Information on ABS came from The Engineering Toolbox and also has additional information (wall thickness, other pipe sizes, etc). Information on CPVC came from a pdf file from Professional Plastics, Inc. It also has more pipe sizes and additional information. If you are unable to view .pdf files, you can ask me for info on a particular pipe size and I can try to find it for you. I tried to do this in a text format with tables, unfortunately this forum does not allow for that sort of advanced coding (I tried HTML and BBCode) so I resorted to making the tables in HTML and then getting screenshots. If anyone has any corrections or additional information, please let me know.