Paper is defined in weight as gsm, with 80gsm being the wight of average copier paper.Card and board are measured in micrometers(microns). A paper is usually classified as a board when it is graster than 220gsm and more often than not is is made from more than one ply. The thickness of card and board can be gauged by the number of ply it consists of, and is measured in microns (1000ths of a millimentre)