Paper Sizes and Formats Explained - The Difference Between A4 and Letter

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Have you ever really taken a look at the packs of computer paper you buy? Or can you automatically eye the standard paper used for letters and academic purposes? You have more than likely heard of A5 or Tabloid, but for many, the only two page sizes that really matter are A4 or Letter. But there exist a number of paper sizes that are relevant to our everyday lives, and knowing them can save you time and money when printing and copying. Thai Unryu Red

The Systems in Existence

Though other paper size standards exist, there are two predominant systems in use today. They are the international and North American systems.

As the term implies, the international standard, also known as the ISO 216 standard, is used throughout the world. It is based on an aspect ratio of the square root of two, like the side of a square and its diagonal. This idea was originally proposed by the German scientist Georg Christoph Lichtenberg in 1786. In 1922, Dr. Walter Porstmann brought Lichtenberg's ideas into being in Germany. This new standard was known as the DIN 476 standard. The system became widely used during World War II. The most commonly used ISO paper size is A4.

The North American system is used primarily in the USA and Canada. The current sizes are based on traditional sizes such as Letter (8.5 in x 11 in) and Legal (8.5 in x 14 in). The names of North American sizes have started with ANSI ever since the adoption of ANSI/ASME Y14.1 by the American National Standards Institute in 1995. Though the sizes now begin with ANSI, they are nevertheless based on the traditional sizes.

ISO 216

The most convenient and distinguishing characteristic of ISO paper is that each format has an aspect ratio equal to the square root of two (1:4142) which makes it simple to enlarge or reduce a document for printing on another ISO paper format. The most popular series of the ISO standard is the A series. The most widely used paper of this series is the A4 format. All paper sizes of this series have a name that consists of an A followed by a number. The larger that number, the smaller the paper.

The basis for the whole system is the A0 format which has an area of one square meter. With an aspect ratio equal to the square root of two, a sheet of A0 paper ends up being 841 x 1189 millimeters. Figuring out the dimensions of the subsequent paper sizes does not require any real mathematical strain since each ensuing size can be created by simply folding the paper in half with the crease parallel to the shortest sides. If you do this with an A0 sheet of paper, the resulting dimensions will be 594 x 841 millimeters, or the A1 format. Take note that the height of A1 is equal to the width of A0.

Two other ISO paper series exist - B and C. The B series was brought into being to provide a wider range of paper sizes, where as the C series is used only for envelopes. The B paper sizes are a bit larger than their A series counterparts and are based on the geometric mean of two consecutive A series sheets. For example, B4 is between A3 and A4 in size, and B5 is between A4 and A5.

The C series was introduced to provide an envelope with enough space for an A series sheet. The sizes of the A series fit in C series envelopes of the same number. That is, a sheet of A4 easily fits into a C4 envelope. The C sizes are just between the A and B series. All of them have a height-to-width ratio equal to the square root of two.

Though these are the main formats of the ISO standard, there are other sizes used for printed items such as labels, business cards, and so on. They are often derived by cutting standard sizes into equal parts. This often leads to sizes with an aspect ratio other than the square root of two.

Simplified Enlargement and Reduction

Many copy machines have preset magnification factors for enlarging or reducing a copied document in order to print it on a different paper size. These presets typically take the form of buttons labelled 'A3 to A4' and so forth. This eliminates wasted margins and saves you the trouble of trying to guess the right magnification factor, which can lead to a heap of misspent paper.