A4 vs Letter: Sizes, and What Actually Breaks

A4 is 210 × 297 mm (8.27 × 11.69 in). US Letter is 8.5 × 11 in (215.9 × 279.4 mm). Letter is about 6 mm wider, A4 is about 18 mm taller, and neither sheet fits inside the other. That last part is the one that costs people real money, because a document designed for one and printed on the other gets silently rescaled or quietly clipped, and everything measured from an edge — margins, fold lines, crop marks — moves with it. Here are the exact numbers, the reason the two systems exist at all, and how to keep a layout intact when it crosses the line.

We build a page-layout app, so we see the aftermath of this more often than we would like: a bulletin that folds a centimetre off centre, a flyer with its footer sliced away, a certificate that came back from the print shop 3 percent smaller than the frame it was meant for. The dimensions are the easy part. What to do about them is the rest of this page.

The short answer

Letter is wider and shorter. A4 is narrower and taller. By area A4 is the larger sheet, but only by about 3 percent, which is small enough that people assume the two are interchangeable and large enough that they are not.

Full dimensions, in every unit you might need

Points are PostScript points, the unit PDFs are actually measured in: 72 points to the inch. Pixel figures are for a full-bleed image with no margin.

Two conversions worth committing to memory, because they explain every other number on this page:

• Letter is 5.9 mm wider than A4 (215.9 − 210). Call it 6 mm, or about 0.23 in.
• A4 is 17.6 mm taller than Letter (297 − 279.4). Call it 18 mm, or about 0.69 in.

An inch is exactly 25.4 mm, so all of the imperial figures above are derived from the metric ones and rounded to two decimals. A4’s “8.27 × 11.69 in” is really 8.2677 × 11.6929 in. That rounding is why you sometimes see A4 quoted as 8.26 or 8.3 inches; the millimetres are the definition, the inches are the approximation.

Why the two systems differ at all

This is the fact that makes everything else make sense, and almost nobody explains it properly.

The ISO 216 A series is built on a single geometric trick: every A size has an aspect ratio of 1:√2, roughly 1:1.414. That ratio is the only one that survives being halved. Cut an A4 sheet across its long side and you get two sheets of exactly the same proportions — that is A5. Halve A5 and you get A6. Go the other way and two A4 sheets make an A3. The whole series is one shape at different scales, and A0 is defined as the sheet with that ratio whose area is one square metre. A4 is A0 folded in half four times.

The consequences are everywhere once you notice them. Print two A5 pages onto one A4 sheet and nothing is scaled or cropped — it just fits. Shrink an A4 poster to A5 and every proportion and margin ratio holds. Booklet imposition and saddle-stitched programmes are trivial in the A series because the maths was designed in.

The North American sizes have no such relationship. Letter is 8.5 × 11 in, an aspect ratio of 1:1.294. Half a Letter sheet is 5.5 × 8.5 in, an aspect ratio of 1:1.545 — a completely different shape. The ANSI series (A = Letter, B = Tabloid, C, D, E) alternates between two aspect ratios as you go up, so it never quite settles. The sizes are traditional rather than derived; they come from historical paper-mill and typewriter conventions, not from a formula.

Neither system is wrong. The A series is easier to scale; Letter is what tens of millions of North American printers, binders and envelopes are already built around, and that inertia is not going anywhere.

What actually breaks when a document crosses the line

Here is the part the dimension tables leave out. When you send a Letter-sized PDF to a printer loaded with A4, one of two things happens, and neither is free.

Option one: the printer scales it to fit. A4 is narrower, so width is the binding constraint. 210 ÷ 215.9 = 0.973, so your page comes out at about 97 percent of its intended size. Going the other way — an A4 document on Letter paper — height is the constraint: 279.4 ÷ 297 = 0.941, so you land at about 94 percent. Those percentages sound harmless. They are not, because scaling is uniform and applies to everything:

• A 20 mm margin becomes 19.4 mm or 18.8 mm.
• 11 pt body text becomes roughly 10.7 pt or 10.3 pt.
• A fold line measured 139.7 mm from the top of a Letter page lands at 135.9 mm on A4 — but the sheet is 297 mm tall, so the fold is no longer anywhere near the middle.
• Crop marks move inward, which means a trimmed piece comes back smaller than the spec you gave the shop.
• Anything registered to a physical object — a window envelope, a pre-printed letterhead, a die-cut, a certificate frame — stops registering.

Option two: the printer prints at actual size and clips. Now nothing is rescaled, which is good, but the 5.9 mm of extra Letter width has to go somewhere. Centred, that is about 3 mm shaved off each edge. If your design has a full-bleed colour band, a footer sitting close to the trim, or a table that runs to the margin, that is where the damage shows up.

The failure we see most often is a folded piece. A half-fold bulletin designed on Letter folds at 139.7 mm from the top. Print the same file on A4 and the sheet is 297 mm tall, so the true centre is 148.5 mm — nearly 9 mm away. Either the printed fold guide no longer matches the physical fold, or the folded piece has a visible lip. If you are building one, our guide to making a church bulletin walks through fold positions in more detail; the short version is that fold measurements must be taken from the page size you are actually printing on.

Scale to fit vs actual size

Every print dialog offers some version of this choice, and the wording differs by app: “Fit to printable area”, “Shrink oversized pages”, “Scale to fit”, versus “Actual size”, “100%”, or “None”.

Use actual size whenever the output has to measure something in the physical world — anything folded, trimmed, bound, mounted, mail-merged onto labels, or matched to a pre-printed form. Use fit to page only when you are printing a reference copy and you genuinely do not care about exact dimensions.

But the real lesson is upstream of the print dialog: exporting at the right page size beats rescaling at print time, every time. Rescaling is a uniform multiplication applied after all your decisions are made. Changing the page size lets you make different decisions — pull a wide header in by 6 mm, spend the extra 18 mm of A4 height on a more generous bottom margin, move the fold to where the paper actually folds. The output looks designed rather than squeezed. When we export a PDF, the page size is baked into the file, so a correctly sized PDF will print at actual size on the right paper without anyone having to think about it.

Set the page size before you start, not after

The cheapest fix for all of this is choosing the right page size on a blank document rather than converting later. Every serious layout tool puts this in document setup; the trick is simply to look at it before you place the first text box.

Korva ships presets for Letter, Legal, Tabloid, A3, A4, A5, B5, postcard, business card, banner and #10 envelope, plus a custom size, and keeps the current one in the status bar rather than three dialogs deep — a visible page size is a page size you notice is wrong. If you are comparing tools, our overview of desktop publishing software covers what else to look for.

When your audience straddles both systems

Plenty of organisations genuinely need one file to work on both sheets: a church with an overseas partner congregation, a nonprofit with volunteers in three countries, a business shipping documentation to both North America and Europe. Producing two versions is the correct answer when you can. When you cannot, design to the overlap.

The shared area of A4 and Letter, both centred, is 210 × 279.4 mm (8.27 × 11 in). That is the A4 width paired with the Letter height — the largest rectangle that fits on both sheets. Everything inside it lands on paper either way.

You still need a printer margin on top of that, because almost no desktop printer prints edge to edge. Allow 10 mm all round and you get a safe live area of 190 × 259.4 mm (7.48 × 10.21 in). Here is how to place it:

Keep every piece of text, every logo, every table edge and every fold guide inside that 190 × 259.4 mm box, and the same PDF prints acceptably on both. Backgrounds and decorative colour can run outside it — they will simply be trimmed or float on a slightly wider band of white, which nobody notices.

Two practical notes. Set the document itself to A4 if you must pick one, because a 97 percent scale on A4 hardware is less destructive than a 94 percent scale on Letter hardware, and A4 users are the larger group worldwide. And avoid folds in a document meant for both systems, since the fold position is the one measurement that cannot be made safe on two different sheet heights. Our free church bulletin templates come in both page sizes for exactly this reason.

A4 vs Letter vs Legal, and the rest of the family

Legal gets dragged into this comparison constantly, so for the record: US Legal is 8.5 × 14 in (215.9 × 355.6 mm) — the same width as Letter, 3 inches longer. It is not a metric size and it has no A-series equivalent; A4 sits between Letter and Legal in height and below both in width. Legal is largely a North American legal-and-contracts format, and it is the size most likely to be missing from an overseas printer’s tray.

The tier above: Tabloid (also called Ledger) is 11 × 17 in, exactly two Letter sheets side by side, and A3 is 297 × 420 mm, exactly two A4 sheets. Both are the standard choice for a folded four-page programme in their respective systems.

The tier below: A5 is 148 × 210 mm — half an A4, and the usual size for a folded bulletin or a small booklet. The Letter-system equivalent is Half Letter at 5.5 × 8.5 in, which, as noted above, is a different shape from Letter rather than a scaled copy of it.

Which countries use which

Letter is the standard in the United States and Canada, and it is in common use in Mexico, the Philippines, Chile and Colombia.

Canada deserves a specific mention because it trips people up. Canada is metric in almost every other respect, but in practice Canadian offices, printers and stationery shops run on Letter. Sending files north from the US, you are fine; sending them from Europe, you are not.

A4 is the ISO 216 standard and is what essentially everywhere else uses: the UK, the EU, Australia, New Zealand, India, and most of Asia, Africa and South America. For an international audience with no other information, A4 is the safer default.

The bottom line

A4 is 210 × 297 mm and Letter is 8.5 × 11 in. Letter is 5.9 mm wider, A4 is 17.6 mm taller, and the A series’ 1:√2 ratio is what makes A4 halve neatly into A5 while Letter does not. Everything painful about the pairing follows from those three facts.

The habit that prevents nearly all of the damage is small: decide the page size before you place anything, export the PDF at that size, and print at actual size rather than fit to page. When your audience spans both systems, design inside 190 × 259.4 mm and stop worrying about it.

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