International paper size standards

International paper size standards, primarily the ISO 216 system, define a series of paper sizes based on a consistent aspect ratio of √2 (approximately 1.41). The most common is A4, measuring 210 × 297 mm, used globally for documents and printing. Sizes are organized into series (A, B, C), with each size doubling or halving in area as you move between them. For example, A3 is double the size of A4, and A5 is half. This system ensures that when you cut or fold a sheet in half, the next size maintains the same proportional aspect ratio.