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The side ratio of one to the square root of two preserves proportions when folded. The figure is taken from ISO, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.

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Mondo Knows Facts

Standard A4 paper uses a unique mathematical aspect ratio

The side ratio of one to the square root of two preserves proportions when folded

International standard paper sizes like A4 are defined by ISO 216 using an aspect ratio of one to the square root of two. This mathematical property means that folding a sheet in half produces a smaller page with identical side proportions. The system allows seamless scaling of drawings and printed text across sizes.

Where this comes from

ISO

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Tags: paper, standards, geometry

Standard A4 paper uses a unique mathematical aspect ratio: the short answers

Where does this come from, and can I check it?: The side ratio of one to the square root of two preserves proportions when folded. The figure is taken from ISO, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
Is this really a everyday life fact?: Yes. It sits on the Everyday Life shelf, one of 1,090 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
What else can I read about it?: The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.