Posters Large format posters can be any size. There are a few proven rules for readability to consider when you are setting your copy. A column of body type should be about 35 to 55 characters. Serif type is best for masses of copy. Save sans serif type for headlines and sub-heads.
Small type is hard to read, particularly for older readers.
Think before using anything smaller than 10-pt. Build in white space with subheads, boxes, generous margins and leading. Avoid non-related graphics. Just because you have some white space doesn't mean you have to fill it with a cute graphic. Leave the white space.