What is A4 paper?

Answer 1

A4 is the standard size of paper used for computer printouts and other uses.

A4 paper is 210 × 297 mm. It has an area of 1/16 square metres.

It is one of a series of paper sizes starting with A0, which has an area of 1 square metre.

Another Answer

The advantage of using A-series of paper sizes is that the height to width ratio remains constant throughout the series. So, if you were to fold an A4 sheet in half, you would have an A5 sheet of identical ratio. Reducing an A4 document to A5 will result in the same proportion of white space around any text area as there was on the original A4 document. This is not the case, for example, with US letter size -if you fold this in half, the ratio of height to width changes significantly making it impossible to reduce any text area in proportion when copying.