A folio usually indicates a large book size of 15" in height or larger when used in the context of a book description.
Further, folio sizes are often sub-divided and described as being one of:
- Crown folio (15" - 18")
- Medium folio (18" - 20")
- Royal folio (20" - 23")
- Elephant folio (23" - 25")
- Atlas folio (25" - 50")
- Double elephant folio (50" and up)
However, folio also has a distinct meaning when describing a type of binding: a folio is a method of binding sheets of paper into
leaves, whereby a single printed sheet of paper is folded once. Several folios are usually laid inside of one another, creating a
gathering which is in turn stitched into a book.
Folio is often abbreviated
fo or
2°.
This
2 volume survey of London from 1720 is a good example of a folio:
