This document describes best practices, based on the experience of experts, for setting appropriate requirements, in specifications and other standards and contract documents, on ferrite content of nominally austenitic or duplex ferritic-austenitic stainless steel weld metals. It also describes a best practice on measurement and measurement reproducibility, and deals with outliers in measurement. It considers ferrite in the weld heat-affected zone of duplex stainless steel. It does not consider specification or measurement of ferrite in ferritic stainless steels nor in martensitic stainless steels.