But where does A4 come from?

Paper formats play a key role in the world of printing. From the large A0, ideal for plans and posters, to the practical A4, ubiquitous in offices and homes, each format is designed to suit a variety of needs. But behind this simplicity lies a rich history and an ingenious design. We explain. 

A legacy of more than two centuries

The origin of A formats dates back to the 18th century. In 1786, the German physicist Georg Christoph Lichtenberg came up with a constant aspect ratio (√2:1) for sheets of paper. This concept was later formalised with the birth of the metric system in 1798, under the impetus of the French Revolution, which sought to standardise measurements in Europe.

However, it wasn't until 1922 that Walter Porstmann, a German engineer, developed the DIN 476 standard. This system laid the foundations for the formats we use today, including A4. In 1975, this standard was adopted worldwide as ISO 216.

The logic behind A formats: from A0 to A4

What sets A formats apart is their geometric design. A0, for example, has an area of 1 m². Folding this sheet in half along its length gives you an A1 (0.5 m²), then an A2, an A3 and finally an A4. This system of division makes it possible to reduce or enlarge formats while maintaining a constant ratio of √2:1.

This means that:

• An A4 corresponds to 1/16th of the area of an A0.
• The linear dimensions of each format decrease by a factor of √2 (around 1.414) compared with the previous one.

Here is an overview of the areas:

• A0 : 1 m²
• A1 : 0,5 m²
• A2 : 0,25 m²
• A3 : 0,125 m²
• A4 : 0,0625 m²

A format designed for practicality

This ingenious system meets specific needs:

• Simplified printing – the constant ratio makes it possible to enlarge or reduce documents (for example from A4 to A3) without altering the proportions.
• Optimised folding – large formats, such as plans, can be folded while retaining their legibility and alignment.
• Worldwide uniformity – an A4 document can be used without further adjustment, whatever the region.

A4, the star of everyday use

With its dimensions of 21 × 29.7 cm, the A4 format is indispensable. It is used for everyday printing, administrative correspondence, teaching materials and marketing documents. A0, for its part, remains the format of choice for posters and technical plans, while the intermediate formats (A1, A2, A3) are suited to specific uses. For example, an A5 can easily be used for a flyer, as with this visual created by the Agency for Chryso.