To many people wordwide, excluding North America and Canada, the most familiar paper size size is A4 (a familiar 210mm x 297mm). It is commonly used for letters and correspondence in the UK and it is the standard paper size for most home printers.
Office paper sizes as Letter, Legal, Tabloid and more. Instead paper formats like "Letter" (8.5 x 11 inches), "Legal" (8.5 x 14 inches), "Executive" (7 x 10 inches), and "Ledger/Tabloid" (11 x 17 inches) are widely used.