We live in a post-WIMP world. The traditional Windows, Icons, Menus and Pointers of the PC graphical user interface are no longer present in many hand-held devices. There has been a dramatic rise in the use of smart phones in particular, with Apple selling their billionth iPhone in 2016. This trend in devices and the shift to touch interfaces has caused concern with regards to usability and has been described by some as a “usability crisis”. This alleged crisis is born out of a proliferation of product features combined with a trend towards minimalisation in user interface style. This means that user interface functions are potentially becoming less visible. The challenge is to try and quantify and understand what is happening with regards to UI visibility, which is deemed to be a critical component creating a usable interface. This paper demonstrates an approach to determining a “visibility score” for a product’s user interface. The approach is applied to the home screen of an iPhone. This produces a visibility score of less than 10% in other words over 90% of the functions available are not visible at the top level. Such a score needs to be treated with caution but can help inform the general debate as well as creating useful insights for the designers of products.