A4

A4 is a standard paper size, defined by the international standard ISO 216.

It is 210 x 297 mm.

There is a myth that this paper format should correspond to the golden mean, which is obviously incorrect, instead you can easily see that:

<math>\frac{297}{210} \approx \sqrt{2}</math>

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A4 is also the actual model number for the German V-2 rocket.