Manufacturing industries using powder metallurgy (PM) techniques – including additive manufacturing (AM) and metal injection moulding – rely on a supply chain of closely specified, high-performance metal powders to produce precision components at a competitive cost. The physical characteristics of these powders – bulk properties and those of the individual metal particles – define their performance and are closely controlled during manufacture. Packing density and flowability are key bulk properties and are directly, though not exclusively, influenced by particle size. Accordingly, it is vital to identify analytical tools that can reliably set size specifications for metal powders, to validate quality and manage their use. Sieving has long been a favoured technique for routine particle sizing. However, it also has many limitations that are addressed by laser diffraction. In this article Dr Sarennah Longworth-Cook and Parminder Singh explore the importance of metal powder particle size, and compare the value of sieving and laser diffraction within this context.