Paper size
From Craft-Wiki
Almost all countries in the world use ISO 216 A4 as their standard paper size, which measures 210 by 297 millimeters (8.27 in × 11.7 in).
A few countries use the Letter (ANSI A) size, which measures 8.5 by 11 inches (215.9 by 279.4 mm).
Each of these two paper sizes can be cut and folded in a specific way to create standard card bases.
