This International Standard specifies the method and apparatus for: - the measurement of the delta ferrite content, expressed as ferrite number (FN), in largely austenitic and duplex ferritic-austenitic stainless steel weld metal through the attractive force between a weld metal sample and a standard permanent magnet; - the preparation and measurement of standard pads for manual metal arc covered electrodes. The general method is also recommended for the ferrite measurement of production welds and for weld metal from other processes, such as gas tungsten arc welding, gas shielded metal arc welding and submergred arc welding (in these cases, the way of producing the pad should be defined; - the calibration o other instruments to measure FN.