国际标准（ISO 216）¹

早在1786年，一位德国的科学家格奥尔格·克里斯托夫·利希滕贝格就发现长宽比为√2的矩形具有许多特点。在20世纪初期Walter Porstmann将此概念应用在一系列纸张尺寸的制定，并且在1922年被制定为德国标准（DIN 476）。随着各国逐渐采用，后来此标准被定为国际标准（ISO 216）。

国际标准的纸张尺寸可分为A、B、和C三种系列。此标准的特色是纸张尺寸的长宽比均为√2（约为1.4142）。同系列但不同尺寸的纸张，其几何比例相同，因此可以直接缩放影印而不会造成纸面图案有边缘裁切的问题。

A PAPER

A系列的制定基础首先是求取一张长宽比为√2且面积为1平方米(m²)的纸张。因此这张纸的宽长分别为 841 毫米和 1189 毫米（长宽比为√2:1），并且编号为A0。若将A0纸张的长边对切为二，则得到两张A1的纸张，其宽长均为 594 毫米和 841 毫米。依此方式继续将A1纸张对切，则可以依序得到A2、A3、A4等等纸张尺寸。在制定标准时，尺寸均以整数为准，因此对切的纸张尺寸若带有小数(小于 1 毫米)则会舍入计算。

The dimensions of the A series paper sizes are defined by the ISO 216 international paper size standard. The A series was adopted in Europe in the 19th century, and is currently used all around the world, apart from in the USA and Canada. The most common paper size used in English speaking countries around the world is A4, which is 210mm x 297mm (8.27 inches x 11.7 inches). The largest sheet from the A series is the A0 size of paper. It has an area of 1m2, and the dimensions are 841mm x 1189mm. The A series uses an aspect ratio of 1:√2, and other sizes in the series are defined by folding the paper in half, parallel to its smaller sides. For example, cutting an A4 in half, will create an two A5 sheets, and so forth. Any size of brochure can be made using paper from the next larger size, for example A3 sheets are folded to make A4 brochures. The standard lengths and widths of the A series are rounded to the nearest millimetre.²

德国在1922年制定了标准DIN 476，同时将尺寸系列增添两项扩充修改。它将A0尺寸的两倍定义为2A0，并将A0尺寸的四倍定义为4A0来使用。

B PAPER

B系列的制定基础首先是求取宽边的长度为1米且面积为√2平方米(m²)的纸张。因此这张纸的宽长分别为 1000 毫米和 1414 毫米（长宽比为√2:1），并将其编号为B0。若将B0纸张的长边对切为二，则得到两张B1的纸张，其宽长均为 707 毫米和 1000 毫米。依此方式继续将B1纸张对切，则可以依序得到B2、B3、B4等等纸张尺寸。和A系列相比，B系列的纸张面积是同号A系列的√2倍，例如B4纸张面积是A4的√2倍。

The dimensions of the B series paper sizes are defined by the ISO 216 international paper size standard. The B series is not as common as the A series. It was created to provide paper sizes that were not included in the A series. The B series uses an aspect ratio of 1:√2. The area of the B series paper sheets is the geometric mean of the A series sheets. For example, B1 is between A0 and A1 in size. While the B series is less common in office use, it is more regularly used in other special situations, such as posters, books, envelopes and passports.

C ENVELOPE PAPER

C系列的制定基础是将A系列和B系列的尺寸作几何平均而求得的。例如C4的纸张尺寸是A4和B4尺寸的几何平均，且纸张长宽比仍为√2:1。这样一来，C4的尺寸系介于A4和B4之间，A4的纸张可以装入C4大小的信封袋中，而C4的纸张可以装入B4大小的信封袋中。

The dimensions of the C series sizes are defined by the ISO 269 paper size standard. The C series is most commonly used for envelopes. The area of C series paper is the geometric mean of the areas of the A and B series paper of the same number. For example, C4 has a bigger area than A4, but smaller area than B4. Therefore an A4 piece of paper will fit into a C4 envelope. The aspect ratio of C series envelopes is 1:√2, and this means that an A4 sheet of paper when folded in half, parallel to its smaller sides, will fit nicely into a C5 envelope. When it is folded twice, it will fit into a C6 envelope, and so on.

D PAPER

1997年修订的中华人民共和国国家标准GB/T 148-1997，大致沿用了ISO 216的规范，但没有规定C系列纸张规格，而是另外增加了D系列纸张规格（长宽比同样为√2:1）。

The dimensions of the Chinese series paper sizes are defined by the GB/T 148-1997 Chinese paper size standard. This standard documents the ISO series, but it does not follow the same principles. Originating from the Republic of China, 1912-1949, the Chinese format is a custom series known as the D series. It is different from the D Series in Sweden. The aspect ratio is approximately √2. The longest side of a Chinese D Series is exactly two times larger than the short side of the next smallest size.

其中D系列尺寸又被称作“标准印张”，从大到小通常依次被称为全开、对开、4开、8开、16开、32开和64开（“开”有时也写作“K”）；A系列由于较D系列尺寸更大，尺寸从大到小通常依次被称为“大xx开”，如A4纸被称作“大16开”。另外，若非通过对折方式进行裁剪，还可以裁剪出3开（362mm × 781mm）、6开（362mm × 390mm）、24开（182mm × 196mm）等规格。GB/T 148-1997的尺寸容许误差与ISO 216相同。

BUSSINESS CARD

The standard business card size used in Europe is 85mm x 55mm, which is a similar size to banking cards, making them easier to store. The standard business card size in the US and Canada is 3.5 inches x 2 inches (89mm x 51mm). It is fairly common nowadays to move away from the traditional rectangular business card, and be more creative by having square and rounded rectangular shapes. The business card based on the ISO 216 standard is the same size as A8 which is 74mm x 52mm.