We study the effort needed for designing Web applications from an empirical point of view. The design phase takes an important part of the overall effort needed to develop a Web application, since the use of tools can help automate the implementation phase. We carried out an empirical study with the students of an advanced university class that used W2000 as a Web application design technique. Our first goal was to compare the relative importance of each design activity. Second, we tried to assess the accuracy of a priori design effort predictions and the influence of some factors on the effort needed for each design activity. Third, we also studied the quality of the designs obtained.