Paper sizes: A4, A3, A2, A5

Standardised paper sizes make our lives easier. For example, when buying A4 stack, we can be sure that it is going to fit any printer designed for home use. Although we use A series paper sizes on a daily basis, very few people know how standardisation had come about and whose idea it had been.

History of paper sizes goes back to 1786, when Georg Christoph Lichtenberg, a German scientist, noticed that rectangular paper with an aspect ratio of √2 (that is, ratio of the longer side to the shorter side) has some unique scaling properties.

Starting with the base A0 size, each subsequent size can be achieved by folding the sheet in half across the longer side and every sheet obtained this way is going to have the aspect ratio of √2, too.

Lichtenberg’s observations gave rise to the international standard ISO 216, which specifies universal paper sizes in the modern world (apart from USA, Canada and parts of Mexico).

ISO 216 paper size	Measurements [mm]	Measurements [in]
A2	420x594	16.5x23.4
A3	297x420	11.7x16.5
A4	210x297	8.3x11.7
A5	148x210	5.8x8.3

Did you know?

A0, the base size for A paper size series, was designed to have an area of 1 square meter (841x1189 mm; 33.1x46.8 in).

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