The clear liquid height on sieve plates has been measured in a hydraulic simulation column. Experimental work and investigation of published data show that three different foaming regimes have to be distinguished, as Chen recognised, and the hole diameter has an influence on the clear liquid height as Dhulesia proposed. The Hofhuis-Zuiderweg correlation has been modified to describe the clear liquid height in the froth, mixed and spray regimes, respectively. Different formulae have been developed for each of the foaming regimes. Two new parameters have been introduced: the hole diameter and the free cross section.