I have chosen the standard film poster size as these posters are used in cinemas and this is the most common time a film poster would be seen. The standard film poster is called 'One-Sheet'
The One-Sheet is definitely the most common among US movie poster sizes, measuring 27 inches by 40 inches. It represents the standard movie poster size used in U.S. movie theaters today.
And here is the other dimensions of different types of film posters.
Still 8 x 10 inches: These are black and white photos, usually with a glossy finish, used for lobby display and press promotion.
Lobby Card (LC): These measure 14 x 11 inches, were printed on light card stock, and were originally made in sets of eight per movie for display in theater lobbies. Most sets have one title card featuring title and production credits plus related artwork. The other seven cards are colored photographic scenes.
Lobby cards are no longer used in the US, but are still sometimes produced for the overseas movie market. Finding complete lobby card sets is not easy, as most desirable title sets have been broken up. Often, sets will have what are termed 'dead' cards—cards that do not feature main actors or scenes.
There are also the so called Jumbo Lobby Cards (JLC) which were made before 1940 and are usually found only as single cards. JLC come in 14 inch x 17 inch size.
Window Card (WC): 14 x 22 inches, are printed on card stock and come flat. These smaller movie posters were usually used for off-site advertising e.g. in windows of local stores in exchange of movie passes. Top four inches were left blank by the printer for the local exhibitor to fill in. For this reason, WC posters are sometimes found with the top 4 inches trimmed off.
There is also—though not so common among movie poster sizes—a Jumbo Window Card (JWC), measuring 22 x 28 inches.
A Mini Window Card (MWC) is also available, measuring 11 x 14 inches; these are also printed on cardboard.
Insert: These measure 14 x 36 inches, are usually printed on card stock and come rolled though many pre-1960 were distributed folded; post-1960 inserts were printed on thinner stock.
1/2 sheet: This is probably the second most popular size among movie poster. It measures 28 x 22 inches, is printed on card stock, and come rolled. Image is usually different from that used on 1-sheet; instead, it is often the same as the first, or title card, in the lobby card set.
Lenticular: These come in approximately the same poster size as the one-sheet (approx. 27 x 41 inches) movie posters with the main difference being thatlenticular posters are printed between composite sheets of plastic and lit from behind to create a 3D/holographic effect.
30 x 40 Heavy Stock Movie Posters: These measure 30 x 40 inches and are printed on heavier card stock. Image invariably is the same as 1-sheet but may be silk screened instead of lithographed. These posters come rolled and do not exist for many film titles.
40 x 60 inches: Printed on heavier card stock, otherwise these are similar to the smaller 30 x 40 heavy stock posters. Image may also have been silk screened, however it often differs from that of the smaller heavy stock movie poster size. These are designed for use outside the theater, on an easel, exposed to the elements. This poster size is often incorrectly referred to as a 2-Sheet.
Banner: These movie posters measure approximately 81 x 24 inches. Older ones were printed on bookbinder's cloth or light card stock. Modern ones are vinyl or light card stock or paper, while banner poster sizes are highly variable.
3-Sheet Movie posters: Often pasted onto the wall outside of theater, 3-Sheet posters measure 41 x 81 inches, and are printed using two sheets of lower stock paper; though rare as it may be, it is also possible to find 3-Sheet posters printed on three separate sheets.
From the 1970s onwards, three-sheets were sometimes printed in one piece and issued as 'international' version.
6-Sheet Movie Posters: 81 x 81 inches, printed on paper stock, usually in four sections, and come folded; for use in larger U.S. theater lobbies and movie palaces, or on the outside of the building. This poster size is not so popular and rare to find.
Billboard or 24-sheet Movie Posters: These massive posters measure approximately 106 x 234 inches, but may come in various poster sizes. As their name suggests, they are for use on roadside billboards and are usually printed on twelve separate sheets.
Information about film posters was taken from http://www.practical-home-theater-guide.com/poster-sizes.html
