A4 vs US Letter: printing PDFs without clipped edges

A4 and US Letter look almost identical on a desk, which is exactly why they cause trouble. The difference is a few millimetres in one direction and almost two centimetres in the other, enough for a printer to cut off a footer, shrink a form so its boxes no longer match, or add a white strip that makes a document look carelessly produced. This guide gives you the exact measurements, explains what your print dialog is doing when it says "fit" or "actual size", and shows how to convert a PDF to the size the recipient expects.

The exact dimensions

A4 belongs to the A series defined by the international standard ISO 216; the EU Agency for Railways' terminology database, for example, defines A4 as 210 × 297 mm under that standard. US Letter is not an ISO size. It is defined in inches, 8.5 × 11, and is the everyday office size in the United States and Canada. Printer manufacturers list both in their specifications; Canon's manuals, for instance, give Letter as 215.9 × 279.4 mm and A4 as 210 × 297 mm.

PDF files measure pages in points. In the default PDF coordinate system one unit is 1/72 of an inch, as Adobe's developer documentation states, so converting is plain arithmetic: millimetres ÷ 25.4 × 72.

Size	Millimetres	Inches	PDF points
A4	210 × 297	8.27 × 11.69	595 × 842
US Letter	215.9 × 279.4	8.5 × 11	612 × 792
Difference	Letter is 5.9 mm wider and 17.6 mm shorter	0.23 in wider, 0.69 in shorter	17 pt wider, 50 pt shorter

The A4 figures in points are rounded: 210 mm works out to 595.28 points and 297 mm to 841.89, which is why software reports A4 as 595 × 842. Letter divides cleanly because 8.5 × 72 = 612 and 11 × 72 = 792.

The shapes differ too. A4 has a height-to-width ratio of about 1.414 (the square root of two, which is what lets A3 fold into two A4s), while Letter is about 1.294. Letter is a slightly squatter rectangle, so one size can never be scaled onto the other without either empty space or cropping.

Why a PDF prints with clipped edges or extra margins

A PDF stores its own page size. The printer has its own paper size. When the two disagree, something has to give, and what gives depends on the scaling option chosen in the print dialog.

• A4 file printed on Letter at actual size. The page is 17.6 mm taller than the paper. Centred, roughly 8.8 mm disappears from both the top and the bottom, before you even count the strip the printer cannot reach. Headers, footers and page numbers are the usual casualties.
• Letter file printed on A4 at actual size. Now the page is 5.9 mm wider than the paper, so about 3 mm is lost on each side, and there is around 8.8 mm of unused paper at the top and bottom. Text set close to the side margins can be clipped.
• Either file printed with scaling to fit. Nothing is cut, but everything shrinks a little and white bands appear on two sides.

There is a second, quieter cause: the printer's own margin. Most desktop printers cannot put ink right to the edge of the sheet. Microsoft's Edge printing help notes that many printers need a minimum margin of around 0.25 inches (6.35 mm) on each side. A PDF that is the correct size can still lose content placed in that outer strip if it is printed at actual size, which is why designers keep important content well inside the edge.

What "fit" and "actual size" actually do

The labels differ between programs, but nearly every print dialog offers the same three choices. Microsoft's description of the Edge dialog is a fair summary: fit to printable area resizes the content to fit inside the area the printer can reach, actual size prints with no scaling, and custom lets you type a percentage.

Option	What happens	Use it when
Actual size / 100%	Page printed at its true dimensions; anything outside the paper or the printable area is lost	File and paper are the same size, and exact measurements matter (forms, scale drawings, labels)
Fit / Fit to printable area / Shrink to fit	Page scaled so all of it lands inside the printable area; small white bands appear	File and paper differ, or the layout runs close to the edge
Custom scale	You choose the percentage	You know the exact factor you need, for example 94% for A4 onto Letter

"Fit" usually shrinks more than the paper difference alone, because it fits to the printable area, not the sheet. Take an A4 page on Letter paper with 6.35 mm margins all round: the printable area is 203.2 × 266.7 mm, and fitting 210 × 297 mm into it needs a scale of about 90%. A 10-point font prints at roughly 9 points. That is fine for a letter, but it matters for anything that will be measured, such as a form with boxes sized for a scanner or a drawing with a scale bar.

On a Mac, Preview has its own setting under Preview > Settings (Preferences in older versions) > PDF called "Define 100% scale as". Apple's guide describes two choices: "Size on screen equals size on printout" or "1 point equals 1 screen pixel". If PDFs print at an unexpected size from Preview, check that setting first.

Convert the page size with Resize PDF

Changing the scaling every time you print is fragile, and it does nothing for someone else who prints your file. If a document is going to be printed or uploaded in a different country, convert the PDF itself. Resize PDF places every page on a new sheet of A4, US Letter, A5 or A3, scales it to fit without distortion and centres it. The pages are embedded as vector content, so text stays sharp.

1. Open Resize PDF and choose the file.
2. Select the target size: A4 for most of the world, US Letter for the United States and Canada.
3. Run it and download the file, which has the size added to its name.
4. Open a page with content near the edges and confirm nothing important now sits too close to the white bands.

Here is what to expect, worked out from the point sizes above:

• A4 to Letter: the page is scaled to about 94% (792 ÷ 842). It fills the full height, and a band of about 26 points (9.2 mm) appears on the left and right.
• Letter to A4: the page is scaled to about 97% (595 ÷ 612). It fills the full width, and a band of exactly 36 points (half an inch, 12.7 mm) appears at the top and bottom.

Resizing changes the sheet, not the design. A form that was laid out for A4 will still look like an A4 form, just slightly smaller on Letter. If the recipient needs a true Letter layout with Letter margins, the only real fix is to change the page size in the original document, such as in Word's layout settings, and export a new PDF.

Trim margins with Crop PDF

Sometimes the problem is the reverse: a PDF has generous white borders, and once it is scaled to fit another paper size the content looks small and lost in the middle. Crop PDF takes the same margin off every edge of every page. You enter the amount in points; 72 points is an inch and about 28.35 points is a centimetre, so the default 30 points trims a little over 10 mm from each edge.

Two cautions. Crop works by setting the visible area of the page, so the trimmed edges are hidden, not deleted; do not use it to remove anything confidential. And because the same margin comes off every side, check the page whose header or page number sits closest to the edge before you print the whole document. A sensible order for a document with wide borders is crop first, then resize, so the scaling works on the content rather than on empty paper.

Print handouts with N-up

Lecture slides and reading packs are often printed two or four pages to a sheet. You can do this in the print dialog, but the result depends on the printer driver. N-up builds the layout into the PDF instead: every output sheet is A4 landscape, split into two columns for 2-up or a 2 × 2 grid for 4-up, with each page scaled to 95% of its cell, which leaves a narrow gutter between neighbours.

The page shape matters more than you might expect:

• Portrait A4 pages, 2-up: each page prints at about 67% of full size, so 10-point text becomes roughly 6.7 points. Readable for most people.
• Portrait A4 pages, 4-up: each cell is wider than it is tall, so a portrait page shrinks to about 34%. 10-point text becomes about 3.4 points, which is too small for most readers.
• 16:9 slides: a wide slide is limited by the cell's width, and the cells are 421 points wide in both layouts. Each slide therefore prints about 400 points (14 cm) wide whether you choose 2-up or 4-up. For slides, 4-up gives the same size as 2-up on half the paper.

Since N-up produces A4 sheets, choose fit to printable area if you print them on Letter paper. The landscape A4 sheet will be scaled to about 94%, which is far kinder than having the outer cells clipped.

Check the page size before you send documents abroad

Visa applications, university admissions, court filings and tenders often go to a country that uses the other paper size. Portals may state the page size they accept, and an office that prints your file will print it on whatever paper is in its trays. A two-minute check avoids a rejected upload or a clipped signature block.

1. Read the requirements. Look for words like "A4 only", "8.5 × 11", "Letter", or margin requirements in the portal's instructions. If none are given, use the size that is standard in the destination country.
2. Check what your file actually is. Open the PDF in a desktop reader and look at Document Properties (Ctrl+D on Windows or Cmd+D on a Mac in many readers). A4 shows as 210 × 297 mm or 8.27 × 11.69 in; Letter shows as 215.9 × 279.4 mm or 8.50 × 11.00 in. Files assembled from scans and exports often mix the two, so check more than the first page.
3. Convert if needed. Run Resize PDF to put every page on the required size.
4. Look at the edges. Open the converted file and check stamps, signatures, page numbers and anything placed within about 6 mm of the edge.
5. Test print one page at actual size on the target paper if you have it. If the recipient will print the file, this is what they will see.

If the document includes a scanned passport page or certificate, resizing is safe: the scan is scaled as a whole, so nothing inside it is cut. What you should avoid is cropping such pages, because official copies are often expected to show the whole original, edges included.