One-Sheets are the standard movie poster size, what you see outside of any movie theater. From 1896 until roughly 1990, almost all actual theater-used one-sheets measured 27" x 41" (since then, most one-sheets measure 27" x 40").

 

Up until 1980 (or thereabouts) the vast majority of one-sheets were folded twice horizontally and once vertically (this is in no way considered a defect). Sometime during the late '70s, studios began printing one-sheets rolled.

 

Most one-sheets after the mid-1980s are printed unfolded, though it is still possible to find some newer posters folded. Most newer one-sheets are printed double-sided (with a mirror image on the back) for use in a light box in front of the theaters. However, sometimes the studios print some posters single-sided.