A4 paper measures 210 mm × 297 mm (about 8.3 in × 11.7 in).

In other words:

  • Width: 210 millimetres (≈ 8.27 inches)
  • Height: 297 millimetres (≈ 11.69 inches)

This is the standard ISO 216 A4 size used for everyday documents, printers, and notebooks in most of the world.