A4 vs Letter: why your PDF prints with the wrong margins

Someone in London sends a document to someone in Chicago. It prints with a strip missing off the bottom, or with margins that look subtly wrong, and nobody can see why because it looks perfect on screen.

This is the A4 and Letter problem, and it affects almost every document that crosses the Atlantic.

The two sizes

Letter is 6 mm wider. A4 is 18 mm taller. Neither fits inside the other, which is what makes this awkward. There is no way to place one on the other without either shrinking it or losing something.

A4 is the international standard, used essentially everywhere except the United States and Canada, which use Letter.

What actually happens

When a printer meets a page of the wrong size it does one of three things, and which one depends on settings nobody usually looks at.

Scale to fit. The page is shrunk slightly (about 94% for A4 onto Letter) so it fits. Nothing is lost, but every measurement is now wrong. Margins are narrower than designed, type is fractionally smaller, and anything that had to be a specific size no longer is. This matters for forms and legal documents.

Print at full size and crop. The page is printed at 100% and whatever falls outside is simply not there. A4 on Letter loses about 18 mm off the bottom, often a footer, a page number, or a signature line.

Refuse and ask. The best outcome, and the least common.

The reason this is confusing is that all three look fine on screen. The PDF is correct; the mismatch only exists at the moment of printing.

Fixing it properly

Set the size at the source. In Word, Layout → Size. In Excel, Page Layout → Size. Do it before exporting, and the PDF is simply correct for its destination.

Change it afterwards if you have to. Resize PDF converts an existing document to a different page size. Be aware that this is scaling, not reflowing: the content is not re-laid-out, it is fitted to the new page. Text will not rewrap and line breaks stay where they were.

Ask before sending anything that matters. For a contract going overseas, thirty seconds of asking beats a reprint.

Designing for both

If a document will genuinely be printed in both places, there is a well-known trick: keep everything important inside the overlap.

The intersection of A4 and Letter is 210 mm wide by 279 mm tall. Design with margins generous enough that all content sits inside that box, and the document prints acceptably on either without cropping anything. Roughly 20 mm side margins and 25 mm top and bottom does it.

This is why so many international forms have wide margins. It is not aesthetics; it is compatibility.

Where it bites hardest

Spreadsheets, because they are usually near the width limit already. A table that just fits on Letter will spill on A4, and the last column ends up alone on a phantom page. Excel to PDF has a fit-to-width setting that removes the problem entirely. Every column lands on the page regardless of paper size.

Forms with signature blocks at the bottom, which is exactly the region A4 loses when cropped onto Letter.

Documents with headers and footers, for the same reason.

Anything with a fixed-size element: a scale drawing, a mailing label sheet, a form with boxes that must line up with pre-printed stationery. For these, scaling to fit is not an acceptable outcome and the page size has to be right.

Checking before you send

Open the PDF and look at its page size. Most readers show it under File → Properties, or in a corner of the window. If it says 210 × 297 mm you have A4; 216 × 279 mm is Letter.

If you are sending abroad and it matters, say which it is in the covering message. It costs one sentence and saves the recipient a puzzled reprint.

Legal, and the rest

Two other sizes worth recognising:

Legal (216 × 356 mm / 8.5 × 14 in) is Letter width but much taller, used for contracts in North America. A Legal document printed on Letter loses a great deal off the bottom.

A3 is exactly twice A4, which is the elegant property of the A series. Each size is the previous one folded in half, and the proportions never change. That is why scaling between A sizes is clean and scaling between A4 and Letter is not.

Why this survives at all

It is reasonable to wonder why two paper sizes this close still exist.

A4 comes from a system where every size has the same proportions and halving one gives the next. Fold A4 in half and you get A5, exactly the same shape. That is a genuinely useful property and it is why the rest of the world standardised on it.

Letter predates the metric system in North American use and is simply what the machinery, the filing cabinets and the software defaults were built around. Changing it would mean changing all three at once, for a gain nobody can see.

So both persist, 6 mm apart in width and 18 mm apart in height, which is close enough that a document made for one looks fine on the other right up until something falls off the bottom.

The three places it goes wrong

Content at the very bottom of the page. A4 is taller. A footer sitting near the foot of an A4 page is below the printable area of a Letter sheet, and it silently vanishes.

Full-bleed backgrounds. A coloured band across the top of an A4 page is 6 mm narrower than a Letter sheet, so you get a white strip down one side.

Anything positioned from an edge. A logo placed 20 mm from the right edge of A4 is 26 mm from the right edge of Letter. Visibly off, especially against something aligned from the left.

The reliable habit

If the document is going to be printed by somebody whose paper you do not know, keep 15 mm of clear space at the bottom and 10 mm at each side. Nothing important goes in that band.

That single rule makes a document print acceptably on either size without you having to know which, and it costs almost nothing in layout. It is what commercial print calls a safe area, and it exists precisely because nobody can control what the other end puts in the tray.