Format is, first and foremost, the imposition scheme (or arrangement) of type on the bed of the press. This, in turn, determines the size and shape of the book, in our case the size and shape of full-length works such as comedias or shorter interludes, such as entremeses.

At the initial printing stage, the compositor took the manuscript (or previously printed work) and came up with the design, i.e., the overall look and length of the suelta to be printed. Designing the text entailed calculating just how many letters/words would make up a forme. The imposition scheme is the arrangement of the formes; the relation of the size and number of pages as they fit on a single sheet of paper. When dealing with the printing of individual plays, this was fairly straightforward.

Bibliographic definition of format is defined by how many times the printed sheet is folded. A printed sheet folded once produces a folio; folded twice, it becomes a quarto; folded three times results in an octavo. This also determines the size and shape of a book. Comedias and saynetes were mostly printed as quartos, while many entremeses and some early 19th-century comedias are octavos.

In bibliographic records, they usually appear abbreviated as (4to) or 4^o; (8vo) or 8^o.

See also: collation, gathering, quire / signature, sheet > leaf/leaves > folio/foliation > pages/pagination, signatures