standard letterhead is
A letterhead is the heading at the top of a sheet of letter paper (stationery). That heading usually consists of a name and an address, and a logo or corporate design, and sometimes a background pattern. The term letterhead is often used to refer to the whole sheet imprinted with such a heading.
International Sizes. There are three ranges of sizes, prefixed A, B and C. The most widely used for general printing and letterhead stationery is the A series. The international letterhead size is an A4. Standard International Paper Sizes.