A4 vs Letter: Why PDF Page Size Matters
They look almost the same on screen, but the size difference is real and it causes actual printing and layout problems.
A4 is 210 × 297mm (595.28 × 841.89 points). US Letter is 8.5 × 11 inches (612 × 792 points). A4 is narrower and taller than Letter. The difference is small enough to go unnoticed on screen but large enough to shift where page breaks fall, cause margins to look uneven when printed on the "wrong" size paper, or clip content near page edges.
The actual numbers
Where this actually causes problems
A document authored for A4 and printed on Letter paper (or vice versa) will have its margins shift — usually shrinking on one edge and growing on the opposite edge, since printers typically center content on the physical page rather than the page size the document was designed for. For text-heavy documents with generous margins, this often goes unnoticed. For anything with content close to the page edge — headers, footers, page numbers, tables that reach near the margin — the mismatch is where clipping or awkward-looking output actually shows up.
Multi-page PDFs assembled from different sources (a scanned Letter-sized cover page combined with A4-sized body pages, for example) can also end up with inconsistent page sizes throughout — usually not something you'll notice until printing or reviewing page-by-page.
How to check before it becomes a problem
Rather than guessing, check the actual dimensions: DocVelora's PDF Page Size Checker reads every page's exact size, matches it to the nearest standard paper size, and flags whether all pages in a document are consistent — useful specifically for catching the "combined from different sources" case before you send or print the file.
If you're about to print a mismatched file right now
Most print dialogs offer two very different options, and picking the wrong one is the actual cause of most A4/Letter printing complaints: "Fit to page" or "Shrink oversized pages" auto-scales the content to the paper in the tray — convenient, but it can slightly distort proportions and shift margins unpredictably. "Actual size" or "100%" prints the page at its true dimensions regardless of the paper loaded — nothing gets distorted, but content very close to the edge on the larger of the two sizes can get clipped. For anything where exact proportions matter (a form, a diagram, a document with fine print near the margin), actual size with a quick margin check beats blind auto-scaling.
If you're printing from Word directly rather than a finished PDF, Word has a built-in "Scale to paper size" option in the print dialog that handles the A4/Letter conversion for that one print job without changing the underlying document — useful when you need a one-off print on whatever paper your printer has loaded.
FAQs
Which one should I use?
A4 almost everywhere outside the US, Canada, Mexico, and a few other countries; US Letter within those. If you don't know your recipient's country, A4 is the more common global default.
Can I convert a PDF from Letter to A4 after the fact?
You can change the page dimensions, but text and layout designed for one size won't automatically reflow to fit the other cleanly — margins may shrink or content may get clipped near the bottom of the page.
Does this affect on-screen viewing, or only printing?
Mainly printing. On-screen, both display at whatever size the viewer window is — the size difference mostly matters once physical paper is involved, or when a design is built to exact page dimensions.
Should I use "Fit to page" or "Actual size" when printing a mismatched file?
"Actual size" (100%) keeps proportions exact but can clip content very close to the edge. "Fit to page" avoids clipping but can slightly distort spacing. For anything where exact proportions matter, actual size with a quick margin check is usually the safer choice.