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, in the 19th century many of the terms started to be used as general indications of a book's height, where "folio" means "big", "quarto" means "ordinary size", and "octavo" means "little". As a result, 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