PDF Page Sizes Explained: A4, Letter, Legal and the Rest

Page size is the invisible cause behind a lot of printing frustration. A document that prints beautifully in London comes out with a white band in Chicago, and nothing in the file looks wrong.

The sizes you will meet

A4 and Letter are close enough to be confusing and different enough to matter: Letter is 6mm wider and 18mm shorter. Print A4 content on Letter and the bottom is at risk; print Letter on A4 and you get a band of white at the foot.

The A series has a useful property

Every A size is exactly half the one before it, folded across the long edge. A4 is half of A3, A5 is half of A4, and the proportions stay identical — which is why scaling between them is clean and why "two A5 pages on one A4 sheet" works perfectly. US sizes have no such relationship, which is why booklet printing there is fiddlier.

Checking what you have

Document properties report the page size — usually of the first page, which is why a mixed document can look consistent when it is not. Page through a long merged pack and look for pages that render at a different width; that is where the print problems will be.

Fixing a mixed-size document

• Print with scale-to-fit, which is the simplest answer and slightly resizes some pages.
• Crop the oversized pages down to a consistent visible size.
• Regenerate the outlying pages at the right size from their source.
• Accept it, if the document is for screen reading only.

Choosing a size when creating a document

Use the standard of your primary audience: A4 outside North America, Letter inside it. For an international readership, A4 is the safer default — a Letter document printed on A4 loses nothing, whereas an A4 document printed on Letter risks the bottom margin.