Most posters should be visible and, more importantly, readable from about two meters away. But how can you test whether its legible without printing off the entire thing, which might itself be a couple of meters of somewhat expensive paper?
A useful test is to print the poster, at reduced size, on a regular sheet of paper, like 8½ × 11”, A4, or maybe legal sized paper. Most graphics programs, and Acrobat Reader, will have a “Shrink to page” somewhere in their print menus. Then, hold the printed page at arm’s length.
You should be able to read the text and make sense of any pictures or graphs, even at this reduced size. In fact, I initially heard that you should be able to read well-designed 35 mm slides at arm’s length, so a regular sheet of paper should easily pass this test.
This won’t pick up a lot of problems, like whether an image will be pixelated when printed at full size, but it is a good way to test whether you’re trying to cram too much stuff on your poster by making everything too small.
Picture by user bondidwhat on Flickr, and used under a Creative Commons license.