Instead of researching decorative part of classical architecture, the interior of St. John’s church was inverted to solid void for compositional, metric and scale analysis. Inverted model helps to understand inner space more clearly, see main compositional, architectonic and structural parts, usually covered with decorative elements. Former main interior elements, such as columns, cornices and altars become the least important ones. The most important case of the inverted model is the scale between side parts and the middle part of the church (the middle part is emphasised by smaller side elements) and clearly seen metric system of window elements.