International Standard (ISO 216):
* A series: A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10 (A0 is the largest, A10 is the smallest)
* B series: B0, B1, B2, B3, B4, B5, B6, B7, B8, B9, B10 (B0 is the largest, B10 is the smallest)
* C series: C0, C1, C2, C3, C4, C5, C6, C7, C8, C9, C10 (C0 is the largest, C10 is the smallest)
North American (ANSI):
* Letter: 8.5" x 11" (most common for everyday use)
* Legal: 8.5" x 14"
* Ledger (Tabloid): 11" x 17"
* Junior Legal: 8.5" x 13"
* Executive: 7.25" x 10.5"
Other systems:
* Japanese: JIS B series (similar to ISO B series)
* British: A series, B series, and C series (slightly different dimensions than ISO)
* Envelope sizes: Various sizes exist, typically named with letters (e.g., #10 envelope)
Note:
* A series paper is based on the square root of 2, with each size having half the area of the previous size.
* B series paper is designed for posters and other large formats.
* C series paper is used for envelopes to fit the corresponding A series paper.
Common Uses:
* A4: Letter-writing, reports, documents, printing
* A3: Posters, blueprints, maps
* A2: Architectural drawings, large posters
* A1: Engineering drawings, large posters
* Letter: Everyday use, documents, printing
* Legal: Legal documents, forms
* Ledger: Spreadsheets, financial statements
The best paper size for your needs depends on the intended use and the application.