How is the A4 paper measured?

A4 paper is measured according to the ISO 216 standard, which defines its dimensions as 210 millimeters in width and 297 millimeters in height (or 8.27 inches by 11.69 inches). This size is part of the A series of paper sizes, with A0 being the largest, and each subsequent size (A1, A2, etc.) being half the area of the previous one when folded in half. A4 is commonly used for letters, documents, and printing in many countries around the world.