Look up paper dimensions in millimetres and inches across ISO A/B series and US sizes (Letter, Legal, Tabloid).
Paper • A/B series · US sizes
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The international A-series (A0, A1, A2 … A4) is defined by ISO 216 and built on an elegant idea proposed by Georg Christoph Lichtenberg in 1786: every size has the same aspect ratio of √2 (≈1.414), so folding a sheet in half yields the next size down with identical proportions. A0 is exactly one square metre, which fixes every other size. North America instead uses traditional "Letter", "Legal" and "Tabloid" sizes that pre-date the metric standard.
Knowing the exact dimensions in both millimetres and inches matters for printing, scaling artwork, setting up documents, and choosing frames or envelopes. This converter lists the full A/B series alongside the common US sizes so you can match or resize between systems without guesswork.