Websites such as McNichols.com, EngineersEdge.com and Harvel.com feature charts of standard pipe sizes, along with links to other articles and tools for use with related plumbing tasks. The Wikipedia page for the Nominal Pipe Size system, the North American pipe sizing standard, also contains a pipe size chart.
The Nominal Pipe Size system consists of a standardized numbering system that allows plumbers, architects and any other related worker to uniformly choose a pipe size for use with high and low temperature and pressure water systems within a building. Each entry in the system is comprised of two numbers that correlate to aspects of the plumbing and building systems, rather than a dimensional measuring of the pipe. One number is the nominal pipe size, which relates to the diameter of the pipe represented in inches, while the other number is a schedule that conveys the thickness of the wall in which the pipe is used.
The Nominal Pipe Size chart on McNichols.com contains the nominal pipe size value and schedule value, alongside additional information to allow a more in-depth measurement of different pipes. This includes both an outside diameter and an inside diameter for pipes, which is helpful for determining if a specific pipe is viable in unique situations.