<P> In the hand press period (up to about 1820) books were manufactured by printing text on both sides of a full sheet of paper and then folding the paper one or more times into a group of leaves or gathering . The binder would sew the gatherings (sometimes also called signatures) through their inner hinges and attached to cords in the spine to form the book block . Before the covers were bound to the book, the block of text pages was sometimes trimmed along the three unbound edges to open the folds of the paper and to produce smooth edges for the book . When the leaves were not trimmed, the reader would have to cut open the leaf edges using a knife . </P> <P> Books made by printing two pages of text on each side of a sheet of paper, which is then folded once to form two leaves or four pages, are referred to as folios (from Latin, foliō, ablative of folium, leaf). Those made by printing four text pages on each side of a sheet of paper and folding the paper twice to form a gathering containing four leaves or eight pages are called quartos (fourths). Similarly, books made by printing eight pages of text on each side of a sheet, which was then folded three times to form gatherings of eight leaves or sixteen pages each, are called octavos . The size of the resulting pages in these cases depends, of course, on the size of the full sheet used to print them and how much the leaves were trimmed before binding, but where the same size paper is used, folios are the largest, followed by quartos and then octavos . The proportion of leaves of quartos tends to be squarer than that of folios or octavos . </P> <P> These various production methods are referred to as the format of the book . These terms are often abbreviated, using 4to for quarto, 8vo for octavo, and so on . The octavo format, with eight leaves per gathering, has half the page size of the quarto format before trimming . Smaller formats include the duodecimo (or twelvemo), with twelve leaves per sheet and pages one - third the size of the quarto format, and the sextodecimo (or sixteenmo), with sixteen leaves per sheet, half the size of the octavo format and one quarter the size of the quarto . The vast majority of books were printed in the folio, quarto, octavo or duodecimo formats . </P> <P> There are many variations in how such books were produced . For example, folios were rarely made by simply binding up a group of two leaf gatherings; instead several printed leaf pairs would be inserted within another, to produce a larger gathering of multiple leaves that would be more convenient for binding . For example, three two - leaf printed sheets might be inserted in a fourth, producing gatherings of eight leaves or sixteen pages each . Bibliographers still refer to such books as folios (and not octavos) because the original full sheets were folded once to produce two leaves, and describe such gatherings as folios in 8s . Similarly, a book printed as an octavo, but bound with gatherings of four leaves each, is called an octavo in 4s . </P>

Book size resulting from folded a sheets to make eight leaves