A4 vs US Letter: sizes, differences and how to avoid scaling

What is the difference between A4 and US Letter?

A4 belongs to the ISO 216 A series used in most of the world. Every A size has the same proportion, the square root of two, so halving A4 gives A5 with the same shape. US Letter is the common North American office size, and the ISO standard itself notes that North America uses different cut size papers.

The difference looks small on paper, but it is enough to move page breaks, clip a footer or push text into a printer's unprintable margin.

Why does fit to page shrink a layout?

A print dialog set to fit or shrink scales the whole page until it fits the selected paper. Because the two formats have different proportions, one dimension always limits the scale. Fitting an A4 page onto Letter is limited by height: 279.4 divided by 297 is about 94.1 percent. At that scale the A4 width becomes about 197.5 mm, leaving roughly 18 mm of unused width across the Letter sheet.

Going the other way, fitting Letter onto A4 is limited by width: 210 divided by 215.9 is about 97.3 percent. The Letter height becomes about 271.8 mm, leaving about 25 mm unused on the A4 sheet. Real print dialogs often shrink further to respect the printer's own margins. A 1 inch square in the original prints noticeably smaller, which matters for rulers, templates, forms and anything that must measure correctly.

How do you print at actual size?

In the print dialog, choose actual size or 100 percent rather than fit or shrink, and confirm the paper size matches the document. Print one page and measure a known dimension with a physical ruler. Do not trust the dialog label alone. Some applications remember the last scaling choice, so check the setting every time you print a proof, especially on a shared office printer where someone else may have changed it. If a page element falls into the unprintable margin, move it inside the layout rather than scaling the whole page down.

For commercial printing the rule is simpler: the file should be built at the exact product size plus bleed, so no scaling is needed. The bleed calculator gives the full document size for either format.

How do you convert a layout between A4 and Letter?

Adapt the layout deliberately rather than stretching it. Never scale width and height by different amounts, because that distorts type, logos and photos.

• Change the page size in the source file, not in the print dialog.
• Keep margins at their original physical size and let text reflow.
• Check every page break, heading and table after reflow.
• Move footers and page numbers up or down to the new edge.
• Recheck photo crops, because the page shape has changed.
• Export and proof each version separately.

If a document will be used in both regions, keep two source layouts. A single file squeezed into both formats usually looks slightly wrong in each.

Which size should you choose for a printed piece?

Choose the size that matches where the piece will be printed, filed and handed out. Letterhead for a United States business is normally Letter, because envelopes, folders and office printers there are built around it. A document sent to European clients may need A4 so it prints correctly on their equipment. Flyers and posters are not tied to office paper at all, so pick the size from the display or distribution method.

The flyer size guide compares the common commercial flyer formats, several of which are neither A4 nor Letter. For stationery, the letterhead design guide covers margins for a printed header and footer.

Does bleed change between A4 and Letter?

The bleed allowance itself is usually the same, commonly 0.125 inch or 3 mm per side, but the resulting file size differs. A Letter flyer with bleed measures 8.75 x 11.25 inches. An A4 flyer with 3 mm bleed measures 216 x 303 mm. Confirm which allowance the printer uses and build the file at that exact size. The GPO guidelines give 1/8 inch as the general minimum.

How do you name the format in a print brief?

State the format by name and by measurement: A4, 210 x 297 mm, or US Letter, 8.5 x 11 inches. A request for a standard page is ambiguous across regions. Name the file with the size, for example "Price sheet Letter v3.pdf", and store both source layouts if both will be reused. That keeps a future update from recreating the same scaling problem.

What is a quick A4 and Letter checklist?

• Decide the format before designing the full layout.
• Set the document size in the source file.
• Print proofs at actual size, not fit to page.
• Measure a known dimension on the physical proof.
• Keep separate layouts when both formats are needed.
• Name the format and measurement in the brief and file name.