Paper Size and Margins That Actually Print

A document that looks right on screen can still come out wrong on paper, and the two settings that decide it are the first two you touch: the size of the sheet, and how much of it you agree to leave empty. Neither is decoration. Both change where every single line breaks.

The document builder asks for both before you type anything, because they are the frame everything else is measured inside. This post covers what the sizes actually are, why A4 and Letter cannot be swapped, what a margin does to a line of text, and the strip around the edge of a sheet that most home printers cannot reach.

A PDF measures everything in points, and a point is one seventy-second of an inch. The paper menu offers six presets plus a custom size typed in points, in portrait or landscape. The presets are these, given as their portrait dimensions:

• A4: 595.28 by 841.89 points. The international standard sheet, 210 by 297 mm.
• Letter: 612 by 792 points, which is 8.5 by 11 inches. The default here, and the standard across the United States and Canada.
• Legal: 612 by 1008 points. Letter's width with another three inches of height.
• A3: 841.89 by 1190.55 points. Twice the area of A4: two A4 sheets joined along their long edge.
• A5: 419.53 by 595.28 points. Half an A4 sheet, which is why two of them print on one.
• Tabloid: 792 by 1224 points. Two Letter sheets joined along their long edge.

Landscape simply swaps the two numbers, so Letter in landscape is 792 points wide and 612 tall. A custom size takes the portrait dimensions in points and the orientation setting still applies on top.

A4 is about 17 points narrower than Letter and about 50 points taller: roughly 6 mm off the width, and 18 mm added to the height. Held side by side that difference looks trivial. Applied to a full page of text it is not, because a narrower column re-wraps every line in the document and the extra height moves where the page break lands.

So choose by recipient rather than by habit: A4 for a reader outside the United States and Canada, Letter inside them. If the document is going somewhere you genuinely do not know, ask. It is a one-line question and it is cheaper than a reprint.

Margins are set either as one of three presets or as four numbers, one per edge. The presets are narrow at 36 points, normal at 72, and wide at 108: half an inch, one inch, and one and a half.

What that arithmetic does to the text is the part worth seeing written down. On Letter paper the normal preset leaves a text column 468 points wide, which is 6.5 inches. Narrow leaves 540. Wide leaves 396. Between the narrowest and the widest preset you have changed the usable width by more than a quarter, and every line in the document re-wraps to match.

The same is true vertically, and it shows up as a page count. Letter with normal margins gives 648 points of usable height per page; narrow gives 720. A letter that sat comfortably on two pages becomes three because you widened the margins, and the preview does it in front of you as you type the number.

One detail that makes the numbers mean what they say: a margin here is measured to the text's em box, so a 72-point top margin puts the first cap-height exactly one inch below the top edge of the paper rather than approximately there.

Most consumer printers cannot put ink all the way to the edge of a sheet. They have to grip the paper in order to move it, and the gripped strip stays blank: commonly a few millimetres on three sides and a little more at the trailing edge. Borderless printing exists on some photo printers and is switched off by default on nearly everything else.

That matters in two ways. The obvious one is that anything inside the strip does not print. The quieter one is that a driver which notices content in the unprintable area will often shrink the whole page to rescue it, which moves every margin on the page inward at once and makes the document smaller than you designed it.

• Keep real content clear of the edges. The narrow preset, at half an inch, is already well outside any normal unprintable strip. A custom margin under about 18 points is where you start gambling.
• Expect a full-bleed colour to fail. A filled shape or a rule drawn to the paper edge prints with a white border, or triggers the scale-to-fit that moves everything else.
• Print one copy before you print forty. The driver decides what happens at the edges, not the file, and drivers differ.

Margins are typed as numbers, so they can be typed large enough to swallow the page. Rather than build a negative content box, the layout collapses the offending pair to zero and says so: a warning strip above the preview reads The side margins left no room for content, so they were ignored. or the same sentence about the top and bottom pair. It is a warning rather than a blocked export, which is exactly why it is worth reading instead of scrolling past.

• A letter, an invoice or a form for a named recipient: their paper. Letter in the United States and Canada, A4 nearly everywhere else.
• A wide table or a long row of figures: Legal, or the same paper turned landscape.
• A handout or a booklet page: A5, which is half an A4 sheet and prints two to a page.
• A drawing, a plan or a very large table: A3 or Tabloid, after checking that the recipient can actually print it.
• Something that has to match an existing document: the custom size, in points, measured from the file you are matching.