Letter vs A4: the two page sizes compared

Two systems, not two versions of one

A4 belongs to the ISO 216 A series, where every size is half the one above and all share a ratio of one to the square root of two. Letter comes from an older North American tradition based on inches and has no halving relationship with the sizes around it. The Cambridge notes on the ISO formats put the difference precisely: A4 is 6 millimetres less wide but 18 millimetres higher than US Letter. They also note that the United States and Canada, and in part Mexico, are the industrialised countries where the ISO sizes are still not widely used. The practical consequence is that scaling between them always changes the shape, not only the size, because 11 divided by 8.5 is 1.29 while A4 is 1.414.

What happens when one is printed on the other

Send an A4 file to a Letter printer without scaling and the bottom 18 millimetres or so fall off the page, which is exactly where footers, page numbers, phone numbers and signature lines live. Choose fit to page instead and the whole page shrinks to about 94 percent, leaving white bands at the sides. Going the other way, a Letter file printed on A4 loses about 3 millimetres from each side unless it is scaled to around 97 percent, which leaves a gap at the foot. Print dialogs often apply these adjustments silently, so a document can look fine in one office and broken in another. Pre printed forms and anything with boxes to fill in by hand suffer most, because the boxes no longer line up.

When the difference matters

For an email attachment read on screen, it barely matters. It matters when paper is involved: flyers printed by a shop, forms that will be filled in by hand, letters sent in window envelopes, documents bound or hole punched, and any template shared between offices in different countries. An Australian or British business sending a proposal to a US client can keep A4, since most readers view it on screen, but a form the client must print and sign should work on Letter. Window envelopes are the strictest case, because the address block has to sit in a position that suits the envelope standard of the country the letter is posted in, and those positions differ between the two systems.

Common mistakes

The most common is designing right to the edges, so any scaling or cropping hits content. Keeping about 15 to 20 millimetres of clear space at the top and bottom lets a page survive either paper. The second is trusting a word processor's default, which follows the language or region setting on the computer, not the country the document is going to. The third is supplying a flyer to a print shop at the wrong size and assuming it will be adjusted; some shops scale automatically and some print exactly what they receive. The fourth is converting a finished layout by stretching it, which distorts logos and photographs because the ratios differ. The last is forgetting that envelopes and folders follow the page standard too.

Letter, A4 and what the builders offer

The flyer builder is A4 based. Its print canvases are A4 portrait at 1240 by 1754 pixels and A4 landscape at 1754 by 1240, alongside six social sizes, and there is no Letter canvas and no custom size. The A4 export is 2480 by 3508 pixels, A4 at 300 DPI, so a flyer headed for a US print shop should either be printed at A4 on Letter with scaling or be laid out with generous top and bottom space so the shop can fit it. The form builder is different: its PDF layout offers A4 portrait, A4 landscape, Letter and a custom size, so a printable form can be produced in the reader's own paper standard. Flyer exports are RGB PDF, PNG or JPG without bleed, so state the finished size when ordering.

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