The perception of the visual complexity of World Wide Web (Web) pages is a topic of significant interest. Previous work has examined the relationship between complexity and various aspects of presentation, including font styles, colours and images, but automatically quantifying this dimension of a web page at the level of the document remains a challenge. In this paper we demonstrate that areas of high complexity can be identified by detecting areas, or 'chunks', of a web page high in block-level elements. We report a computational algorithm that captures this metric and places web pages in a sequence that shows an 86% correlation with the sequences generated through user judgements of complexity. The work shows that structural aspects of a web page influence how complex a user perceives it to be, and presents a straightforward means of determining complexity through examining the DOM.