Choosing a page size and margins

Every other option in the converter is a preference. The page size is a decision, and it changes everything downstream: how many pages you get, how large the type reads, whether it prints correctly, and whether you spend the whole book pinching and panning.

The reason it matters so much is that the two things you might do with the file want opposite answers.

For paper: match the tray

A4 if you are anywhere except the US and Canada. US Letter if you are.

That is the whole rule, and it is not a preference. It is a physical fact about the paper in your printer. A4 is 210 × 297mm; Letter is 216 × 279mm. Print a Letter-sized PDF on A4 and you lose 6mm off the width and gain 18mm of white at the foot. Print an A4 one on Letter and the reverse. Neither is catastrophic, and neither looks right.

A5 is worth knowing about. It is exactly half an A4 sheet, which means you can print two pages to a side and cut, and you get something the size and proportion of an actual paperback. It uses more sheets than A4 but far less paper per word than you would guess, because A4 at a readable type size wastes a lot of line length.

B6 is smaller again, close to a mass-market paperback, and the one to use if you’re printing a booklet onto US Letter rather than A4. There’s a whole guide on that: printing an ebook as a folded booklet.

Trade paperback, 6 × 9 inches, is what most print-on-demand services use. Pick it if the PDF is going to one, and check their template first because some want bleed and a wider inner margin than anything here produces.

A note on the A series

A4, A5 and B6 aren’t arbitrary. Each A size is exactly half the one before it, folded across the long edge, and they all share the same proportions. That’s why two A5 pages fit an A4 sheet with nothing left over, and why you can keep halving without ever having to trim.

US paper sizes don’t work this way. Half a Letter sheet is 8.5 × 5.5in, which is a different shape from Letter, so a two-up print always involves either waste or a different page size. B6 is the closest practical match, which is why it’s here.

For screens: match the screen

Here the instinct almost everybody has is wrong, so it is worth being explicit.

If the text is too small on a tablet, make the page smaller, not the type bigger.

A PDF reader scales the whole page to fit the screen. So:

• 11pt on A4 gives you about 90 characters per line, on a page then squeezed onto a 10-inch display. The type arrives tiny.
• 14pt on A4 gives you about 70 characters per line, on a page squeezed to the same size. Slightly bigger type, a third more pages, still not comfortable.
• 11pt on a phone-shaped page gives you about 35 characters per line. When that narrow page is scaled up to fill the screen, every character is nearly three times the size it was in the first case.

Same type size, completely different reading experience. The page size is the zoom control; the type size barely moves the needle.

So: Tablet screen (4:3) for an iPad or most Android tablets. Phone screen (16:9) for a phone. Both match the shape of the display, so a page fills it with no letterboxing.

The full argument, with the arithmetic laid out, is in reading a PDF comfortably on a tablet or phone.

Line length is the thing you’re really setting

Underneath all of this sits one number that typographers have argued about for a century: how many characters fit on a line. Somewhere around 60 to 75 is the range most people find comfortable in a book. Much below 45 and the eye jumps lines too often; much above 90 and it loses its place coming back to the left margin.

Page size and type size are the two controls you have, and they push that number in opposite directions. A bigger page holds more characters per line; bigger type holds fewer. Which means:

• A4 at 11pt lands around 90. Too wide, which is why A4 documents feel like documents rather than books.
• A4 at 14pt lands around 70. Correct measure, but the type is now large-print size, because you got there by inflating the letters rather than narrowing the column.
• A5 at 10pt lands around 65. This is a paperback, and it’s no accident that paperbacks are that size.

If a page ever looks subtly wrong and you can’t say why, count the characters on a full line. It’s usually that.

Margins

Normal is right for almost everything.

Narrow if you are printing something long and care about the paper, or if you are reading on a screen. Screen margins are wasted space, since nobody holds a tablet by the paper.

Wide if the pages are going into a ring binder, comb or coil. The punched edge takes about 15mm, and Normal margins put your text right up against the holes. Wide is also the one to pick if you intend to write in it.

Type size, briefly

• 10pt — dense. Fine for reference material you scan rather than read.
• 11pt — a book. This is the default and it is the default for a reason.
• 12pt — comfortable, and about 10% more pages.
• 14pt — genuine large print.

One warning: type looks larger on a backlit screen than it does on paper, and almost everyone judging on a monitor picks one size too small. Print two pages before you commit.

Justification, and when to turn it off

Justified text has a straight right edge. It’s what a printed book looks like, it’s on by default here, and on A4 or Letter it’s the right choice.

At small page sizes it stops being the right choice, and the reason is hyphenation. Proper typesetting breaks long words across lines so a justified column can keep even spacing. This converter doesn’t hyphenate. On a wide page there’s enough slack in the spaces that you’d never notice. On A5 or a phone-shaped page there isn’t, so a line ending in a long word has to open its spaces up to reach the margin, and you get visible rivers of white running down the paragraph.

Rule of thumb: A4, Letter and 6 × 9 justified; A5, B6, tablet and phone ragged-right. Look at a couple of pages either way and pick the one that looks less strange.

The settings, as three recipes

Printing at home. A4 or Letter, normal margins, 11pt, justified on, everything else default. Set the print dialog to Actual size.

Reading on an iPad. Tablet screen, narrow margins, 11pt, justification off, page furniture off. The header and footer eat a meaningful share of a small page.

A booklet you’ll fold and staple. A5, normal margins, 10pt, justification off, page furniture on. Then let the printer driver do the imposition.

A rough sense of length

At 11pt with normal margins, an average novel of 100,000 words comes out at roughly:

• A4 — 170 pages
• A5 — 300 pages
• Trade paperback — 320 pages
• Tablet — 240 pages
• Phone — 600 pages

The converter shows you its own estimate as soon as you change the setting, which is more accurate than this table because it has counted your book rather than an average one.

Two things the estimate is useful for beyond curiosity. If you’re printing, it tells you how much paper you’re committing to before you commit to it. And if you’re making a booklet, it lets you nudge the type size until the count lands on a multiple of four, which saves the printer inserting blanks wherever it feels like.