Letter vs A4 in PDF page sizing

Screens hide page size. Every viewer scales the page to the window, so Letter and A4 both look full. Paper does not scale. When the page size in the PDF does not match the paper in the tray, the print driver either shrinks the page or cuts part of it off.

The numbers

PDF measures pages in points, 72 to the inch.

Letter is 16.72 pt (5.9 mm) wider. A4 is 49.89 pt (17.6 mm) taller. The shapes differ too. Letter’s height is 1.29 times its width; A4’s is 1.414, the square root of 2, which is why an A4 sheet folded in half is an A5 sheet of the same shape.

Printing an A4 PDF on Letter paper

• Fit to page. The driver scales the page to 94.1% so its height fits into 11 inches. The width shrinks by the same factor, to 560 pt, which leaves about 9 mm of extra white on each side. 10 pt text prints at 9.4 pt. A barcode or a form box that must be an exact size no longer is.
• Actual size. Nothing is scaled, and 17.6 mm of the page height does not fit. If the printer centers the page, roughly 8.8 mm comes off the top and the bottom. If it aligns to the top, all of it comes off the bottom, which is where footers and page numbers live.

Printing a Letter PDF on A4 paper

• Fit to page. The page is scaled to 97.3% to fit the narrower width. 10 pt text prints at 9.7 pt, and a band of about 12.6 mm of white appears at the top and the bottom.
• Actual size. The page is 16.72 pt wider than the paper, so about 3 mm is lost at each side if centered. Most documents have side margins wider than that, so actual size usually works in this direction. Check anything with content close to the edges, such as tables and full-width headers.

Check what a PDF actually uses

• In a desktop viewer, the Document Properties panel shows the page size (in Acrobat, Preview’s inspector, and the Firefox PDF viewer, among others).
• On the command line, pdfinfo -f 1 -l 999 file.pdf from poppler-utils prints the size of each page in points, with a name such as “letter” or “A4” when it matches.
• A PDF can mix sizes. Checking page 1 is not enough for a merged packet.
• Rotation is reported separately. On our five-page merged test packet, pdfinfo listed pages 1 and 2 as 612 x 792 pts (letter), pages 3 and 4 as 595.276 x 841.89 pts (A4), and page 5 as 792 x 612 pts (letter) with a rotation of 90. Page 5 is stored landscape and turned by the viewer, so it appears upright on screen. A printer driver that ignores the rotation, or a tool that reads only the stored size, will treat it as landscape.

How mixed sizes end up in one file

• Merging documents from different regions. A US offer letter plus a scan from a European office. Merge PDF keeps every page at its original size: in our test, a Letter plus A4 merge produced a file with both sizes unchanged, to the hundredth of a point.
• Photos converted with Fit. Fit makes each page the shape of the photo. Twelve 4032×3024 phone photos became 1440×1080 pt pages in our test, which is 20×15 inches.
• Regional defaults. Word processors default to the paper size of the system’s region, so two people exporting the same template can produce different sizes.

Photos into PDF

JPG to PDF offers Fit, A4, and Letter. A4 and Letter place the image on a standard sheet without stretching it, and they turn the sheet to landscape for landscape photos. Our landscape test photos produced 841.89×595.28 pt pages with A4 and 792×612 pt pages with Letter. If a form asks for an A4 PDF, or the recipient will print it, choose the sheet size rather than Fit.

Fix it at the source

The clean fix is to produce the document at the right size in the first place, not to scale it afterwards:

• In a word processor, set the paper size in page setup before exporting. Margins of at least 13 mm (0.5 in) on every side survive either paper with room to spare, which makes a document forgiving when you do not know where it will be printed.
• In a print-to-PDF dialog, choose the paper size explicitly instead of accepting the default.
• For a mixed file you cannot re-export, print it to PDF on the target paper with “fit to page”, and accept the 94% or 97% scale.

Which one to use

Use the paper size of the place the document will be printed. In the United States, Canada, and Mexico that is usually Letter. Most other countries use A4. When a form or a portal specifies a size, follow it; some document-handling systems reject or rescale pages that do not match. When nobody specifies, generous margins and a consistent size across all pages avoid nearly every problem on this page.

How we measured

Page sizes were read with pikepdf from files produced by this site’s Merge PDF and JPG to PDF tools on 27 September 2026. The scaling percentages and margins are calculated from the standard page dimensions above.