Why your PDF prints too small, too big, or with the edges cut off

Three culprits, in order of likelihood

• The printing application is scaling. By far the most common cause, and the only one where the PDF is entirely innocent. A dialog set to "fit to page" or "shrink to fit" rescales every page before sending it, quietly, every time.
• The page size does not match the paper. A4 and US Letter look similar on a screen and are different shapes on paper. When they meet, something has to give — and the printing software decides what, not you.
• The content runs outside the printable area. Printers cannot print to the physical edge of the sheet. A design with content flush to all four sides will always lose a strip, and no scaling setting fixes it.

There is a fourth possibility worth ruling out early: the page itself may be rotated or carry an odd box. If one document misprints and everything else is fine, check that instead of the printer settings.

A4 and US Letter are not the same shape

A4 is 210 by 297 mm. US Letter is 216 by 279 mm. Letter is therefore slightly wider and noticeably shorter, and the two have genuinely different proportions — roughly 3 per cent wider and 6 per cent shorter, which is enough to matter once you try to make one fill the other.

The point of the table is that none of these are errors. They are the arithmetic of two different rectangles. A document converted from one to the other always leaves a white band along one pair of edges, because you cannot fill a Letter sheet with A4 content without either cropping something or distorting it.

The scaling setting nobody reads

Print dialogs offer several variations on scaling, and the differences are large. Read the current value before changing anything in the document.

The printable area is genuinely smaller than the paper

A desktop printer cannot lay ink right up to the edge of a sheet, because the mechanism has to hold it. The unusable strip is typically 3 to 6 mm on an inkjet and around 4 to 5 mm on a laser, and it applies on all four sides.

This is why a document with a coloured border or a footer at the very edge always looks wrong when printed, even at the correct size. Cropping in the reader, or shrinking the page, will not help — the page is being sent correctly and the printer simply cannot reach that far. The fix belongs in the design: keep content at least 10 mm from the trim edge, and more if it will be bound.

Full-bleed printing exists, but it means printing on a larger sheet and trimming, which is a commercial print job rather than a desktop one.

Measure the document before touching the printer

Two numbers settle most of these arguments: the size of the page as the file defines it, and the size of the paper in the tray. The first is visible in the reader's document properties, usually as a page size in millimetres or inches. The second is written on the ream.

If they disagree, you have found the cause and the fix is either a scaling setting or a different tray. If they agree and the output is still wrong, the problem is the printable area or rotation, not the size. Either way, you now know which half of the system to change, and you will not waste an afternoon resizing a document whose size was never the issue.

When resizing the document is the right fix

Sometimes the document genuinely should be a different shape — a bundle of scans that came back as a mix of Letter and A4, or a form that must be filed on one paper size. Resizing each page is then the right move, and the choice of mode matters more than the size you pick.

• Fit scales the page until all of it sits inside the target, adding white margins where the proportions differ. Nothing is lost, and it is the right choice almost every time.
• Fill scales until the page covers the target, so the overflow falls outside and is effectively cropped. Use it only when you know the content has margins to spare.
• Stretch scales width and height independently to fill the target exactly. It distorts circles into ovals and changes letterforms. In practice there is almost no correct use for it.

One thing resizing cannot do is add resolution. Scaling a page up makes the existing pixels larger; it does not create new ones. A 150 dpi scan enlarged to fill a bigger sheet prints larger and no sharper, and past a certain point it prints visibly soft. If sharpness at the final size matters, the honest answer is to scan again at that size rather than enlarge afterwards.

Why cropping often beats scaling

The most common complaint in the other direction — "the print is tiny with a huge white border" — is usually not a page-size problem at all. It is a page whose content occupies a small part of a large sheet, because it was scanned or exported with generous margins baked in.

Rescaling the whole page to fill the paper enlarges everything including the empty margins, and if the page is already at the correct size the printer will fight you. Cropping the margins instead changes the ratio of content to sheet, so the same content sits on the same paper at a bigger effective size without any scaling at all.

A concrete example: an A4 page carrying a 160 by 247 mm block of text surrounded by 25 mm margins. Printed "fit" on Letter, the whole thing shrinks to about 94 per cent and the text block comes out around 150 by 232 mm. Crop 20 mm from all four sides first and the page is 170 by 257 mm, so it now fits Letter almost exactly, the scaling goes away, and the text block prints several per cent larger for free.

Before you press print

• Check the page size in the document against the paper in the tray. These are the two numbers that matter.
• Set scaling to fit-to-page rather than actual size, unless you know the document was designed for this exact paper and printer.
• Turn off "choose paper source by page size" unless mixed sizes are deliberate; it silently pulls from another tray instead of scaling.
• For anything with a border or a footer near the edge, assume 5 mm will be lost on every side.
• For a document that mixes paper sizes, normalise the pages first — mixed sizes misbehave under every scaling option.
• If the print is too small, try cropping the margins before you try enlarging the page.