You can buy and download the latest editions of AGA Report No. 3 (Parts 1–4) through the American Gas Association (AGA) Store or the Accuris Standards Store .

The standard is a copyrighted professional document. While some older versions are available via public archives, the current, official versions should be sourced through recognized standards organizations:

The AGA 3 standard is subdivided into four critical parts to help users manage specific technical requirements: Focus Area General Equations & Uncertainty Guidelines Fundamental math and error margins. Part 2 Specification & Installation Requirements Physical setup: pipe lengths, orifice plate design. Part 3 Natural Gas Applications Practical industry-specific implementation. Part 4 Implementation Procedure Step-by-step algorithms for software development. Software for AGA 3 Calculations

Since the manual calculation of the "Coefficient of Discharge" or "Expansion Factor" is incredibly complex and requires iteration, most professionals use dedicated software rather than manual spreadsheets. Popular tools available for download include: The Importance of the AGA 3 Standard in Gas Measurement