Posters usually start at A4, then A3, A2 and beyond. The largest poster we have ever produced was 14 metres wide x 6 metres deep. The most common size we produce is A2. They are a one sided piece and can be printed on anything from an inexpensive piece of paper to an expensive, long lasting outdoor synthetic paper. They can be tall and thin, short and wide… there are really not a lot of rules here.