A test method for measuring adsorbed molecular contamination uses a test structure that includes a substrate comprising a plurality of separated test sites having a plurality separate thicknesses having a base design thickness and a designed thickness interrelationship. The test structure is exposed to a molecular contaminant environment to provide an adsorbed molecular contaminant layer upon each of the plurality of separated test sites. The plurality of separated test sites with the adsorbed molecular contaminant layer thereon is measured. An appropriate algorithm that considers the designed thickness interrelationship is used to determine at least one of: (1) the base design thickness; and (2) a thickness of the adsorbed molecular contaminant layer.