The Standard Plumbing Code provides a sizing example in their codebook. The Standard Plumbing Code, the BOCA code, and the International Plumbing Code have joined together and your local code office may have any variation of these three codes in effect, so check your local codes carefully. A factory is the building chosen for their sizing exercise. The instructions provided in their sizing example and explanations is good. By using the tables provided and the formulas given, you can size the water distribution system for the building with minimal stress.
The responsibility of sizing a large water system may never be placed on your shoulders. Architects and engineers will probably design most of the systems that you install in large buildings. But, it does pay to understand the concepts behind sizing a system. Work through the examples I’ve provided above until you are comfortable with the procedure. Once you get the hang of it, sizing a system is not terribly difficult.
