Many paper size standards conventions have existed at different times and in different countries. Today there is one widespread international ISO standard (including A4, B3, C4, etc.) and a local standard used in North America (including letter, legal, ledger, etc.). The paper sizes affect writing paper, stationery, cards, and some printed documents. The standards also have related sizes for envelopes.
Most industry standards express the direction of the grain last when giving dimensions (that is, 17×11 inches is short grain paper and 11×17 inches is long grain paper), although alternatively the grain alignment can be explicitly indicated with an underline (11×17 is short grain) or the letter "M" for "machine" (11M×17 is short grain). Grain is important because paper will crack if folded against the grain: for example, if a sheet 17×11 inches is to be folded to divide the sheet into two 8.5×11 halves, then the grain should be along the 11-inch side. Paper intended to be fed into a machine that will bend the paper around rollers, such as a printing press, photocopier, or typewriter, should be fed grain side first so that the axis of the rollers is along the grain.Loose sizes
The U.S., Canada and Mexico use a different system of paper sizes compared to the rest of the world. The current standard sizes are unique to that continent (though with globalisation other parts of the world have become increasingly familiar with them). The traditional North American inch-based sizes differ