1.1 ,These test methods use air permeability to determine an envelope-specific surface area and its associated average equivalent spherical diameter (from 0.2 to 75μ,m) of metal powders and related compounds. The powders may be analyzed in their “,as-supplied”, (shipped, received, or processed) condition or after they have been de-agglomerated or milled by a laboratory procedure (“,lab milled”,) such as that specified in Practice B859. The values obtained are not intended to be absolute but are generally useful on a relative basis for control purposes.