The most common standards—US Letter and A4—dominate global document formats, but the divide is striking. A4, the international standard under ISO 216, is used by most countries globally, however, the US and Canada continue to stick with the US Letter format, a legacy of historical practices and industrial design.

This split is more than just a matter of size—it’s a reflection of the metric vs. imperial systems, where A4’s metric measurements make it easier for global coordination, while US Letter’s persistence highlights regional resistance to standardization. Despite the global adoption of A4, some countries like Mexico and the Philippines use a hybrid system due to strong ties with the US.

This mix of A4 and US Letter can create challenges in international document sharing, with mismatched margins and scaling often leading to inefficiencies.