Bibliographic format

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Bibliographic format refers to the proportional relationship between a full sheet of paper and the folded and cut leaves of a book. For example, a text printed two-up so that the sheet of paper needs to be folded once to make the leaves of a book is in "folio" format. A book printed four-up on a sheet that's folded in half, then in half again, is a "quarto" and so on.

Confusingly, many of the same terms were also used as standard paper size names (similar to the way "letter" and "legal" are used as paper sizes in the United States today). Even more confusingly, many of the same terms came to be used as general indications of a book's height, beginning in the 19th century. In the context of book height, "octavo" means "little", "quarto" means "ordinary size", "folio" means "big", and "elephant folio" means "huge"). When someone at the Folger refers to "a folio," you have to rely on context to know if that means an oversize book, a book in in folio format, or one of the first four editions of Shakespeare's collected plays.

Abbreviations and names for formats include:

DCRM(B)[1] Gaskell[2] Ordinary spoken English Latinate spoken English Other
full-sheet 1⁰ broadsheet, full sheet
fol. 2⁰ folio folio fo., 1/2⁰, f⁰, F
4to 4⁰ quarto quarto 1/4⁰, Q⁰, Q
8vo 8⁰ octavo octavo 1/8⁰, O
12mo 12⁰ twelvemo duodecimo 1/12⁰, D
long 12mo long 12⁰ long twelvmo long duodecimo
16mo 16⁰ sixteenmo sextodecimo 1/16⁰, S
18mo 18⁰ eighteenmo octodecimo 1/18⁰, T
24mo 24⁰ twenty-fourmo vicesimo-quarto 1/24⁰
long 24mo long 24⁰ long twenty-fourmo long vicesimo-quarto
32mo 32⁰ thirty-twomo trigesimo-secundo 1/32⁰, Tt
48mo 48⁰ forty-eightmo quadragesimo-octavo Fe
64mo 64⁰ sixty-fourmo sexagesimo-quarto 1/64⁰, Sf
72mo 72⁰ seventy-twomo
96mo 96⁰ ninety-sixmo
128mo 128⁰ one-twenty-eightmo

NB. for search-and-replace updating:

  • character following the number may be:
    • degree symbol
    • superscript zero
    • superscript lower-case letter "o"
  • be careful of the order of operations, e.g. change "12⁰" to "12mo" before changing" 2⁰" to"fol." or you'll end up with "1fol."


  1. Descriptive Cataloging of Rare Materials (Books), the international standard for rare books in library catalogs.
  2. Philip Gaskell, A New Introduction to Bibliography. Reprinted with corrections in 1995. New Castle, Del.: Oak Knoll Press, 2007