The 120 film allows several image formats, the most common being the 6 x 6 cm (120 square format), or more exactly 56 x 56 mm. Rectangular formats 6 x 9 cm (120 full-frame format) and 6 x 4.5 cm (120 half-frame format) are also standard. Additionally 6 x 7 cm, and even 6 x 8 cm are used.
The 120 is a typical roll film format. The bobbin was originally made of wood with metal flanges, later all metal, and finally plastic. Frame number markings for the three standard image formats are printed on the backing paper.
There are 12 exposures per film when using 6 x 6 format, 15 for 6 x 4.5, 10 for 6 x 7, 9 for 6 x 8 and 8 for 6 x 9.
The term 645 format is often used now as reference to an ordinary 120 or 220 film used in the 6 x 4.5 cm image format. Due to better control of frame space, modern 645 format cameras get 16 exposures per roll of 120.
The 120 format was originally intended for amateur photography. It has been superceeded in this role today by the 135 film, but is still popular for professional use.
220, introduced in 1965, is the same format as 120, but with double length film and thus twice the number of exposures per roll. Unlike the 120, there is no backing paper behind the film itself, just a leader and a trailer. This means that there is no printed frame numbers, thus forbidding its use on old cameras that use the red window as frame indicator. The film alone being thinner than a film with a backing paper, depending on camera type a special pressure plate may be required to achieve optimal focus.
The 620, introduced by Kodak in 1931 as an intended alternative to the 120, is essentially the same film on a sligtly different all metal bobbin (120 was wood cored at that time):
International standard: ISO 732