Foolscap folio (commonly contracted to foolscap or folio) is paper cut to the size of 8 1⁄2 × 13 1⁄2 inches (216 × 343 mm) (for "normal" writing paper, 13 × 8 in (330 × 200 mm)). This was a traditional paper size used in Europe and the British Commonwealth, before the adoption of the international standard A4 paper.
A full foolscap paper sheet is actually 17 × 13 1⁄2 inches (432 × 343 mm) in size, and a folio sheet of any type is half the standard sheet size or a subdivision of this into halves, quarters and so on.
Foolscap was named after the fool's caps and bells watermark commonly used from the fifteenth century onwards on paper of these dimensions. The earliest example of such paper that is firmly dated was made in Germany in 1479. Unsubstantiated anecdotes suggest that this watermark was introduced to England in 1580 by John Spilman, a German who established a papermill at Dartford, Kent. Apocryphally, the Rump Parliament substituted a fool's cap for the royal arms as a watermark on the paper used for the journals of parliament.
In Brazil, the 8 1⁄2 by 13 inches (215.9 mm × 330.2 mm) paper size is usually named Folio, and it is also sometimes called Ofício II, a reference to the 8 1⁄2-by-14-inch (215.9 mm × 355.6 mm) paper size (which is named Legal but in Portuguese is better known as Ofício).
In Venezuela, the 8 1⁄2 by 13 inches (215.9 mm × 330.2 mm) paper size is named Oficio. While laws expressly permit any paper size, public offices require all documents to be presented in Oficio paper size.
Ring binders or lever arch files designed to hold Foolscap folios are often used to hold A4 paper (210 × 297 mm, 8 1⁄4 × 11 3⁄4 in). The slightly larger size of such a binder offers greater protection to the edges of the pages it contains.