A resistive sensing system is provided for determining the size of print media which has been loaded into an input member inkjet printing mechanism for printing. The media is typically has length and width dimensions, and the printing mechanism has sliding length and width size adjusters which are pushed into contact with the media edges to secure the media in the input member for printing. The length and width size adjusters each have sliding contacts which engage an energized conductive strip at a location corresponding to the position of the size adjusters. The printing mechanism has a controller that interprets an electrical signal received from the sliding contacts to determine what size of media is loaded in the printing mechanism. An inkjet printing mechanism having such a resistive media size sensing system is also provided, along with a method of determining the size of media loaded into the printing mechanism.