A4 vs US Letter: which page size to choose

A4 is 210 × 297 mm, or about 8.27 × 11.69 in. US Letter is 8.5 × 11 in, or about 215.9 × 279.4 mm. A4 is narrower and taller; Letter is a little wider and shorter.

Their areas are close, within a couple of percent, which is why the two are so often confused. The shape is what differs: A4 follows the square root of two ratio used by ISO paper sizes, so cutting an A4 sheet in half gives two A5 sheets of the same proportions.

A4 is the standard across most of Europe, Asia, Africa and South America, and it is the default in most office software outside North America. US Letter is standard in the United States and common in Canada.

The practical rule: choose the size your recipient prints on. A PDF that will only ever be read on screen can use either, because the page scales to the window anyway.

Printing a Letter-sized document on A4 paper, or the reverse, makes the printer fit the page. That usually means a small scale factor and slightly wider margins, so nothing is lost but nothing lands exactly where it was designed to.

In this converter a mismatch never stretches an image: Fit the whole image scales it proportionally inside the margins. Crop to fill is the option that removes content, and the preview shows how much would go.

For something that will be printed and filed, match the paper in the office that will handle it. For scans, labels and anything measured in millimetres, original image size is usually truer to the source.

The page size guide works through how A4, Letter and original image size are calculated, including the 96 PPI fallback. If the document has many pages, combining the images covers order and naming.