Every book format in Shelvd — from broadsheet to 128mo — with dimensions, history, and practical identification tips.
What "Format" Means
A book's format describes how the original printed sheets were folded to create the pages. A folio is folded once (2 leaves, 4 pages), a quarto twice (4 leaves, 8 pages), an octavo three times (8 leaves, 16 pages), and so on. The format determines the approximate size of the book, but not its exact dimensions — those depend on the original sheet size.
This is why "large octavo" and "small quarto" are not the same thing, even if the books are the same height. The format tells you about the construction; the dimensions tell you about the size. Both matter.
How to Identify Format
For books printed before 1900, you can often determine the format by:
- Chain lines — Hold a page to the light. In a folio, chain lines are vertical. In a quarto, horizontal. In an octavo, vertical again.
- Watermark position — The watermark's location in the leaf reveals the fold pattern.
- Gathering size — Count the leaves in a typical gathering. Gatherings of 4 = quarto, 8 = octavo, etc.
For modern books, format is largely academic — machine-made paper and modern printing have detached the term from its original meaning. But the vocabulary persists, and the sizes remain roughly consistent.
The Major Formats
Broadsheet / Broadside
Folds: None — a single unfolded sheet, printed on one side. Typical height: Varies with sheet size. Use: Proclamations, ballads, posters, newspapers.
Folio (2°)
Folds: 1 fold → 2 leaves → 4 pages per sheet. Typical height: Over 30 cm (12"). Use: Large, prestigious works. Atlases, Bibles, early Shakespeare. The format that says "this book is important."
Quarto (4to)
Folds: 2 folds → 4 leaves → 8 pages per sheet. Typical height: 25–30 cm (10–12"). Use: Standard size for quality publications from the 16th–18th centuries. Shakespeare's individual plays were printed as quartos. Academic journals still use this size.
Octavo (8vo)
Folds: 3 folds → 8 leaves → 16 pages per sheet. Typical height: 20–25 cm (8–10"). Use: The most common format for books since the late 18th century. The novel, the general non-fiction title, the "normal" book.
Duodecimo (12mo)
Folds: Creates 12 leaves → 24 pages per sheet (complex fold pattern). Typical height: 17–20 cm (6.5–8"). Use: Smaller books, pocket editions, popular fiction. Common in the 18th and 19th centuries.
Sextodecimo (16mo)
Folds: 4 folds → 16 leaves → 32 pages per sheet. Typical height: 15–17 cm (6–6.5"). Use: Small books, devotional works, travel guides.
Vicesimo-quarto (24mo)
Folds: Creates 24 leaves per sheet. Typical height: 12.5–15 cm (5–6"). Use: Very small books, pocket almanacs.
Tricesimo-secundo (32mo)
Folds: 5 folds → 32 leaves → 64 pages per sheet. Typical height: 10–12.5 cm (4–5"). Use: Miniature books, devotional works.
Sexagesimo-quarto (64mo) and 128mo
Folds: 6 or 7 folds. Typical height: Under 10 cm (4"). Use: Novelty miniatures. At 128mo, you need good eyesight and possibly a magnifying glass.
Sub-Formats and Modifiers
Each major format can be qualified:
| Modifier | Meaning |
|---|---|
| Crown | From a crown-size sheet (~20×15") |
| Demy | From a demy-size sheet (~22.5×17.5") |
| Royal | From a royal-size sheet (~25×20") |
| Imperial | From an imperial-size sheet (~30×22") |
| Large | Larger than standard for the format |
| Small | Smaller than standard for the format |
| Foolscap | From a foolscap-size sheet (~17×13.5") |
| Post | From a post-size sheet (~19.5×15.5") |
| Medium | From a medium-size sheet (~23×18") |
| Super Royal | From a super royal sheet (~27×20") |
So "Crown Octavo" is an octavo from a crown sheet (~7.5×5"), while "Royal Octavo" is an octavo from a royal sheet (~10×6.25"). Same number of folds, different sheet, different result.
Shelvd's 76 Formats
Shelvd includes 76 format options covering all standard and sub-formats. When you select a format in the book form, the system knows the expected height range. This helps with:
- Validation — flagging unlikely dimension/format combinations
- Search — filtering by format across your collection
- Description — the ISBD catalog entry includes the format designation
If you're unsure of the format, measure the book's height and work from there:
| Height | Likely format |
|---|---|
| Over 38 cm | Folio or larger |
| 30–38 cm | Folio |
| 25–30 cm | Quarto |
| 20–25 cm | Octavo |
| 17–20 cm | Duodecimo |
| 15–17 cm | Sextodecimo |
| Under 15 cm | 24mo or smaller |
These are approximations. The actual format depends on the sheet size, not the book height. But in practice, height is a reliable shortcut for post-1800 books.
A Note on Modern Publishing
Modern publishers don't think in formats. They think in trim sizes: "6×9 inches," "B-format paperback," "trade paperback." These correspond roughly to traditional formats (6×9 is a large crown octavo, for instance), but the terminology has shifted.
For cataloging purposes, Shelvd lets you record both the format designation and the exact dimensions. Use the format for bibliographic convention and the dimensions for precision. They complement each other.
See also: Physical Description · Glossary · Octavo, Quarto, Folio (blog)