A “sheet of paper” usually means either A4 (most of the world) or US Letter (mainly the USA and a few others). Both are close in size but not identical.

Quick Scoop

Common everyday sizes

  • A4 sheet (international standard)
* 210 × 297 mm
* 21.0 × 29.7 cm
* About 8.3 × 11.7 inches
  • US Letter sheet (used in the USA, etc.)
* 8.5 × 11 inches
* About 216 × 279 mm

So if you ask “how big is a sheet of paper?” the answer depends on where you are: in most countries it’s A4, in the US it’s Letter, and they’re similar enough that they look almost the same at a glance.

Handy comparison (at a glance)

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Type Size (mm) Size (cm) Size (inches) Where it’s common
A4 210 × 297 mm 21.0 × 29.7 cm ≈ 8.3 × 11.7 in Europe, UK, most of world
US Letter 216 × 279 mm 21.6 × 27.9 cm 8.5 × 11 in USA, Canada and a few others

A good mental picture: an A4 sheet is just slightly taller and narrower , while US Letter is a bit shorter and wider. They’re close enough that many people don’t notice unless they’re lining pages up for printing or filing.

TL;DR:

  • Most of world: A4 = 210 × 297 mm (about 8.3 × 11.7 in).
  • USA & a few others: Letter = 8.5 × 11 in (about 216 × 279 mm).

Information gathered from public forums or data available on the internet and portrayed here.