A4 vs Letter Size: The Difference and Why Printing Goes Wrong

A4 measures 210 by 297 millimetres, which is 8.27 by 11.69 inches. US Letter measures 216 by 279 millimetres, or 8.5 by 11 inches. Letter is about six millimetres wider and A4 is about eighteen millimetres taller. Both differences are small enough that a stack of each looks identical on a desk, and large enough that a document laid out for one and printed on the other will not land where the designer intended. Almost every cross-border printing complaint traces back to these two numbers.

The geographic split is straightforward. The United States, Canada and Mexico use Letter as the default, along with parts of the Philippines and Chile. Essentially everywhere else follows ISO 216, the A-series standard, of which A4 is the office workhorse. The A-series has a property Letter lacks: every size has an aspect ratio of one to the square root of two, so folding an A3 sheet in half yields exactly A4, and scaling between sizes never changes the proportions. That is why European documents scale cleanly between formats and American ones do not.

Trouble appears at the print dialog rather than at the design stage. When a printer is loaded with Letter and receives an A4 document, the driver typically applies fit to page, shrinking everything by roughly 94 percent. Margins move inward, font sizes drift slightly, a footer sitting close to the bottom edge can be pushed off, and a document that ended cleanly on page four may spill a stray line onto page five. In the other direction, an A4 tray receiving a Letter document leaves an unbalanced strip of white at the bottom and can clip the right edge.

Prevention is cheap if you do it early. Set the page size when you start writing, not when you print, and set it to the recipient's regional standard rather than your own. After exporting, check the PDF's actual page dimensions in the document properties instead of trusting the source application. Keep critical content, especially signature lines, page numbers and table borders, at least fifteen millimetres inside the trim edge so a scaling event cannot reach it. If you have inherited a PDF at the wrong size, crop can normalise the page box before printing.

The decision rule: match the paper standard of the country where the document will be printed, not the country where it was written. When the audience is genuinely mixed and you cannot produce two versions, design inside the intersection of the two formats, which is 210 millimetres wide by 279 millimetres tall, and disable scale to fit in the print dialog. Anything laid out inside that safe area prints correctly on both trays without the driver having to resize a single element.