ESDU 72009 enables the pressure drop to be estimated for liquid or gas flow. A reference pressure drop that is a function of gauze porosity is first predicted. An empirical factor corrects that reference pressure drop for the effect of Reynolds number less than 2000 (based on wire diameter); that factor is unity for higher Reynolds numbers. Another empirical factor that is a function of porosity and Mach number corrects the pressure drop in gas flow for compressibility; two forms are given@ one of which yields the static pressure drop while the other yields the total pressure drop across the gauze. The data can be applied to square- or rectangular-mesh gauzes. Sources are listed of information on the effect of supersonic flow@ choking and inclining the gauze to the flow.