ISO paper standards are widely used. Originally for the litho and screen print industries where sizes need to be fixed they are still used extensively in the large format digital printing market although Large format digital printers use rolls rather than sheets of paper. This is due to the fact that most of the shelf display hardware for exhibition, retail and advertising are manufactured to take these set poster sizes. Poster frames, Billboards, Pavement signs come in set sizes. European displays are metric where in the UK we still have imperial sizes such as 20" x 30".