A4 paper is a common paper size, defined by the International Organization for Standardization, with dimensions of 21 centimeters by 29.7 centimeters (210 millimeters by 297 millimeters). The aspect ratio of A4 paper is the square root of 2:1, which means that if you fold an A4 paper along the long edge, you can get two A5 papers, which also have the same aspect ratio. A4 paper is the standard paper size used in most countries in the world, and it is often used for printing, copying, writing, drawing, etc. The area of A4 paper is about 0.062 square meters, and the weight varies depending on the different grammages, usually between 60 grams and 120 grams.