Where does this come from, and can I check it?

Every other size in the A series is cut down from that single area. The figure is taken from International Organization for Standardization, 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 2,600 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.

Mondo Knows Facts

A0 paper is defined as exactly one square metre

Every other size in the A series is cut down from that single area ISO 216 begins with A0, a sheet of one square metre in the ratio one to the square root of two, and makes each smaller size by halving the longer edge. Sizes are rounded to whole millimetres, so A4 is 210 by 297 millimetres and weighs about 5 grams at 80 gsm. Grammage measures a square metre, not the sheet in your hand. It sits in Mondo's everyday life collection, one of 200 facts that each trace back to the reference below.

Where this comes from

International Organization for Standardization

Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.

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Standard A4 paper uses a unique mathematical aspect ratioThe side ratio of one to the square root of two preserves proportions when folded Standard C4 envelopes are sized to fit flat A4 paper sheetsISO envelope series measurements allow flat A4 documents to slide in smoothly Fluorescent tube numbers measure eighths of an inchThe T8 label means a tube one inch wide, which is about 25 millimetres Cheap paper yellows because of leftover ligninLight and oxygen turn wood residues into acidic groups that darken the sheet Corrugated cardboard derives strength from a wavy fluted middle layerPaper arches sandwiched between flat liners cushion impacts and resist weight Cardboard toilet paper cores were introduced in the late 1800sCylindrical core tubes maintain roll shape for smooth bathroom dispensing

Tags: paper, standards, measurement

A0 paper is defined as exactly one square metre: the short answers

Where does this come from, and can I check it?: Every other size in the A series is cut down from that single area. The figure is taken from International Organization for Standardization, 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 2,600 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.