A4 paper size vs Letter. The difference is minimal, but important: A4 is a little taller, while Letter is a little wider. … There is a good reason why most countries have accepted the ISO 216 series of paper sizes (the official grouping which includes A4) as a standard.
Similarly one may ask, is 8.5 x11 paper called letter?
As offices became increasingly mechanized with the introduction of the typewriter, photocopier and printer, the need for paper at a fixed size grew, and 8.5 x 11 inches became standard “letter” paper.
Also, should I use letter or A4? Unless you have a very strong US-biased group of clients, use A4. A4 is an international standard, while Letter is only used in the US and Canada.