Legal paper dimensions are only to be officially found in the USA and Canada, as these are the only two countries which have not officially adopted the ISO standard paper sizes. The most commonly used sizes are known as Letter, Legal, Ledger and Tabloid. (Letter size is also known as "American Quarto" outside the USA). There are numerous other sizes and shapes of page, but these are the most commonly used.
The legal page size is 8.5" x 14" (216mm x 356mm), as shown in the plan below.