American Measurement Standard

The American Measurement Standard, or AMS, is a voluntary guide for measuring, calculating, and reporting square footage in residential dwellings. Its 2020 edition was compiled by a consensus of real estate agents, appraisers, assessors, home builders, and architects.

Like ANSI Z765, the AMS measures from the exterior dimensions of a house. It sorts all of a home's space into eight reporting categories and sets out definitions for finished square footage and gross living area, with many illustrations and worked examples.

A state appraisal board approved the AMS for use in January 2019. It is a separate document from ANSI Z765, and on loans sold to Fannie Mae, ANSI Z765 is the standard appraisers are required to follow.

Further reading: American Measurement Standard on Wikipedia.