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A4 and Letter paper sizes steeped in history

The following article is reproduced with permission from the October 2007 Newsletter of Serif (Europe) Limited, a software company based in Nottingham.


Whether using Serif products or not, most of us will have encountered documents in both A4 and Letter sizes.  They’re similar, so why do both standards exist?  Get comfy.

A4 (210 x 297mm) doesn’t jump out as a metric size, but it is of course part of a metric standard, set in 1975,* and based on a German standard from 1922.  A key feature of the standard is that A4 is half the size of A3, which in turn is half the size of A2 and so on up to A0, the largest in the range.  And at 84.1cm x 118.9cm, A0 is 1m2 of paper.  As metric paper weights are usually measured in grammes per square metre it makes mass calculations easy for standard paper sizes across paper and publishing industries.  The A-series also has another big trick up its sleeve . . .

At 1m2, why isn’t A0 just 1m x 1m rather than being as it is, a fancy size in odd numbers of millimetres?  Because when a 1m x 1m square is halved (the most efficient way to produce new sizes from large paper sheets), the new rectangular size no longer has the same shape as the original, so any artwork resized during reproduction would either be massively stretched to fill the rectangle, or it just wouldn’t fill the page.  Not great.  Halve it again and the paper becomes square again, so there would be two very different shapes of paper through the range’s sizes.  However, for A-series paper, smaller sizes are still half the previous paper size in every case, but the width-to-height ratio is the same for the whole series, 1 : 1.41. This means an A4 page can be scaled up by 141% and all the artwork and text is the perfect width and height to fill an A3 page.  Similarly, scaling A4 artwork down to 71% of its original size will see it fit perfectly on an A5 page with no unpleasant stretching or squashing of artwork required; all the sizes are the same basic shape.  This ‘magic number’ for paper aspect ratio, 1 to the square root of 2, was first suggested in 1786.

Letter paper, common throughout the USA, Canada, Mexico and a few other countries, at 8.5” x 11” (216 x 279mm), is a similar shape to A4.  Although in use for longer, it became a recognised standard in 1921 to reduce waste in industry, at the same time that the US government used another agency’s standard to decide on a slightly smaller page for official use.  Letter didn’t become the official national standard paper size for US government until the early 1980s.  The largest paper size in the popular range, 17” x 22”, was a legacy from manufacturing limitations of a few hundred years ago when paper was made by hand.  From this large size, the paper was halved and quartered to make modern Tabloid (11” x 17”) and US Letter (8.5” x 11”) sizes.  The early days of print are a rich heritage indeed, but Letter paper may not survive globalisation.

Unlike the A-series paper sizes, this range doesn’t have a ‘magic number’ aspect ration to make the range’s sizes all the same shape as each other – but they are not so differently shaped as to make things unworkable when switching from one size to another. As global business, research and information sharing is all on the up, the A-series is increasing in popularity in North America.  It may become a global standard in future, but until then we’re pleased to say that Serif products support a wide range of sizes for everyone, with easy editing tools to make and change artwork to suit all layouts!

© Serif (Europe) Limited 2007 -

Pat Kennedy adds: The 1975 date appears suspect for the introduction of the A-series?  See reference in HMSOldies Information Circulars January-February 2007 to Alan Dodson’s Standards for Authors and Printers, which was the HMSO official guide published in 1959 showing the range of service-wide stationery designs for the newly introduced paper sizes of A5 and A4.

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