The "Great Divide": A4 vs. US Letter

One of the most common frustrations in printing occurs between the international A4 and the American Letter size.

They look similar, but they are not compatible. US Letter is wider and shorter (216mm x 279mm) than A4 (210mm x 297mm). This means if you print a document formatted for A4 on US Letter paper, the top or bottom of the page will likely get cut off.

The Magic of the ISO 216 Standard (A-Series)

Most of the world uses the ISO 216 standard, based on the metric system. The logic is brilliant: every sheet in the A-series has an aspect ratio of 1:√2.

This means if you cut an A0 sheet in half, you get two A1 sheets with the exact same proportions. This scaling property allows you to resize designs from A4 to A3 or A5 without any content getting cut off.

History of British Sizes: What is "Foolscap"?

Before the adoption of the metric system, the UK used Imperial sizes. The most famous is Foolscap (8.0 x 13.0 inches).

It derived its name from a watermark used in the 15th century depicting a court jester's cap (a "fool's cap"). While A4 has largely replaced it, you will still find "Foolscap Folios" and binders in the UK legal profession.