The size of paper can vary depending on the standard used. The most widely used paper size for general printing and letterhead stationery is the A series. The most common of these sheet sizes is the international letterhead size A4, which measures 8.27 inches × 11.7 inches or 210 x 297 mm
. In the United States, the standard paper sizes are Letter (8.5 × 11 inches) and Legal (8.5 × 14 inches)
. The A series paper sizes are defined by the ISO 216 international paper size standard, which is used across the world except in North America and parts of Central and South America
. The A series uses an aspect ratio of 1:√2, and other sizes in the series are defined by folding the paper in half, parallel to its smaller sides
. The North American paper sizes are based on traditional formats with arbitrary aspect ratios
