[Pharo-project] How to know 'real' extent of a PanelMorph

Hello, I have a panelMorph composed by several row/columns with different kind of morphs. What I would like to know is, what is the extent / size that I should use to FULLY display this panel (without scrollbars). Each time I ask for the extent of a panelMorph, it answers 50@40, whatever what is inside. If you openInWorld you will have something very very small. Is there a way to retrieve an extent with which the panel morph will be 'well' displayed (without having scrollbars everywhere)? In other words, what I really want to know is: Given two panelMorph, is there a way to say that one need more place than the other to be displayed?