A4 paper size, widely used in the United Kingdom and Europe, is measured as 210 mm by 297 mm. This is the size typically used for letters and other correspondence.

A3 paper is larger (yes, as the numbers get smaller, the sheets of paper get bigger), measuring 297 by 420 mm. And A2 paper is larger yet, measuring 420 x 594 mm, which few personal printers can handle.

You may notice that one edge of each paper is double the next smaller size. For instance, A4 measures 210 by 297mm, while A3 measures 420 mm on the long edge. 420 is double 210. That’s because each smaller sheet is calculated on half the dimensions of the larger.

For instance, fold an A3 sheet in half on the long edge (420 mm), and you’ll have a sheet of A4, measuring 210 mm by 297 mm. A0 paper, the paper from which all these other sizes are created, measures 841 mm by 1189 mm, which measures one square meter.

A3 paper is larger (yes, as the numbers get smaller, the sheets of paper get bigger), measuring 297 by 420 mm. And A2 paper is larger yet, measuring 420 x 594 mm, which few personal printers can handle.

You may notice that one edge of each paper is double the next smaller size. For instance, A4 measures 210 by 297mm, while A3 measures 420 mm on the long edge. 420 is double 210. That’s because each smaller sheet is calculated on half the dimensions of the larger.

For instance, fold an A3 sheet in half on the long edge (420 mm), and you’ll have a sheet of A4, measuring 210 mm by 297 mm. A0 paper, the paper from which all these other sizes are created, measures 841 mm by 1189 mm, which measures one square meter.