A4 paper is the size most used in the world. It is used as the classic paper sheet in all industrialized countries, and beyond, except in North America, which has retained different standards.

The dimensions of A4 is 297 x 210 mm or 11.69 x 8.27 inches. It has an area of 0.062 m², which corresponds to 0.07 square yards, 0.65 square foot, or 93 square inches. When usual and recommended printing margins are put , the printable size of A4 is 247 x 170 mm.

Compared to A0, which is the largest size standardized by ISO 216, A4 is 16 to 1, that is to say that one A0 sheet contains 16 A4 sheets. This proportion can also help to measure the weight of an A4 sheet. Indeed, A0 strictly measure 1 m². However, paper weights are expressed in g/m². So we know that for a paper of 160 g/m², an A4 sheet weighs 160/16 = 10 grams.

A4 is somehow the "star" of ISO 216. When it inherited in 1975 from Portsmann and his DIN 476 (1922), itself derived from the imagination of Professor Lichtenberg (1786), it had to be decided on a format that can correspond to a household and professional use. A4 was obviously the right size for these purposes.

Today, it is used for all printing, letters, magazines, forms ... that can be found in everyday life.

A4 is a half an A3, quarter an A2, for larger sizes, and corresponds to 2 A5 sheets, 4 A6 sheets or 8 A7 sheets for smaller sizes

A4 is majoritly used for letters, pinting documents, magazines ...