The ANSI standards for engineering seems to be always published in a table form like this http://en.wikipedia.org/wiki/Nominal_Pipe_Size but it looks like a really limited way of displaying results. Why is it that there isn't any formulas we can use to compute the results rather than look up loads of tables? I am quite sure these values are calculated from some physics formulas (actual values) and engineering principles (safety margin etc). Anyone to enlighten me please? Thanks.