Book sizes

Publishers size books by trade convention. A novel, a textbook and a coffee-table book each have a customary trim size, and the names come from two traditions: the folded-sheet names of hand-press printing (folio, quarto, octavo) and the modern format letters used in British publishing.

The three UK paperback formats are the ones most people meet. A format (110 × 178 mm, 4.33 × 7.01 in) is the mass-market pocket paperback. B format (129 × 198 mm, 5.08 × 7.8 in) is the standard trade paperback for fiction. C format (135 × 216 mm) is the larger paperback that usually matches the hardback. In the United States the common trade sizes are 6 × 9 in (152.4 × 228.6 mm, the octavo) and 5.5 × 8.5 in (Half Letter).

The old names work by folding. A folio (304.8 × 482.6 mm here) is a sheet folded once to make two leaves; a quarto (241.3 × 304.8 mm) is folded twice into four leaves; an octavo three times into eight. Duodecimo (12mo, 127 × 187.3 mm), 16mo, 18mo, 32mo and smaller follow the same logic with more folds. Because the result depends on the sheet, octavos come in named sizes: Crown octavo (136.5 × 203.2 mm), Medium octavo (165.1 × 234.9 mm), Royal octavo (165.1 × 254 mm), Imperial octavo (209.6 × 292.1 mm) and Super octavo (177.8 × 279.4 mm).

Book sizes sit near, but not on, ISO sizes. B format is a little larger than B6 (125 × 176 mm); C format is close to A5 (148 × 210 mm) but narrower and taller. The Crown, Demy and Royal octavos take their names from the British Imperial sheets they were cut from.

A practical tip: print-on-demand services quote inch trims, and 6 × 9 in, 5.5 × 8.5 in and 5 × 8 in are the cheapest to produce. Spine width depends on page count and paper caliper, so ask the printer for the exact figure before designing the cover.

Choosing a trim size

Readers recognise genre by shape before they read a word, so the trim size is a positioning decision. Mass market paperbacks are small and cheap to ship. Trade paperbacks are the default for literary fiction and non-fiction. Larger formats read as textbooks, manuals or art books, and a novel printed at that size looks like neither.

The practical constraint is what your printer supports. Print-on-demand services each publish a list of trim sizes, and a size outside that list means offset printing and a minimum order in the hundreds.

Page count changes everything

A smaller trim size means more pages for the same words, and page count drives both unit cost and spine width. The same manuscript can run 240 pages at one trim and 320 at another, which changes the price band and the shelf presence.

Spine width is calculated from page count multiplied by paper thickness, so it cannot be finalised until the interior is. Get the spine measurement from the printer rather than estimating it, because a cover printed to the wrong spine wraps visibly off-centre.

Margins and the gutter

Inner margins need more room than outer ones, because the binding swallows part of the page. Perfect-bound books need a larger gutter as page count rises, since a thick book does not open flat.

Saddle-stitched booklets have the opposite problem: creep pushes the inner pages outward as the fold thickens, so the outer margin narrows towards the centre of the book. The imposition calculator handles the page ordering.

What drives the price

Page count first, then colour: a single colour page in an otherwise black-and-white book can move the whole interior to a colour price. Paper stock and binding follow. Trim size itself matters less than people expect, except where it pushes you off a printer's standard list.