The Difference Between A4 and Letter Paper Sizes and Formats Explained

Have you ever given the packets of computer paper you buy a second thought? Or do you have a natural instinct to look at conventional letter and academic paper? You’ve probably heard of A5 and Tabloid, but for many people, A4 and Letter are the only page sizes that count. However, there are a few paper sizes that are important in our daily lives, and understanding them may help you save time and money when printing and copying.

Currently Existing Systems

Though there are various paper size standards, there are two that are widely used today. The international and North American systems are the two.

The international standard, also known as the ISO 216 standard, is utilised all over the globe, as the name suggests. It is based on a square root of two aspect ratio, similar to the side and diagonal of a square. Georg Christoph Lichtenberg, a German physicist, first presented this concept in 1786. Dr. Walter Porstmann popularised Lichtenberg’s views in Germany in 1922. The DIN 476 standard was the name given to this new standard. During World War II, the method was frequently deployed. The A4 paper size is the most regularly used ISO paper size.

The North American system is mostly utilised in the United States and Canada. The existing sizes are based on standard sizes like Letter (8.5 in x 11 in) and Legal (8.5 in x 14 in) (8.5 in x 14 in). Since the American National Standards Institute adopted ANSI/ASME Y14.1 in 1995, the names of North American sizes have began with ANSI. Despite the fact that the sizes now start with ANSI, they are still based on the conventional standards.


The most useful and distinctive feature of ISO paper is that each format has an aspect ratio of square root of two (1:4142), making it easy to enlarge or shrink a document for printing on another ISO paper format. The A series of ISO standards is the most widely used. The A4 format is the most extensively used paper in this series. This series’ paper sizes all have a name that begins with an A and ends with a number. The smaller the paper, the higher the number.

The A0 format, which has a one-square-meter surface area, serves as the foundation for the whole system. A sheet of A0 paper measures 841 x 1189 millimetres when the aspect ratio is equal to the square root of two. The dimensions of the successive paper sizes may be calculated without much difficulty since each size can be made by folding the paper in half with the crease parallel to the shortest sides. If you use an A0 piece of paper, the measurements will be 594 x 841 millimetres, which is the A1 size. Keep in mind that A1’s height is the same as A0’s width.

There are two further ISO document series: B and C. The B series was created to accommodate a larger variety of paper sizes, whereas the C series is solely used for envelopes. The B paper sizes are based on the geometric mean of two successive A series sheets and are somewhat bigger than their A series counterparts. B4 is the size between A3 and A4, while B5 is the size between A4 and A5.

The C series was created to allow adequate room in an envelope for an A series sheet. The A series sizes are compatible with C series envelopes of the same number. That instance, an A4 page fits perfectly inside a C4 envelope. The C sizes are located in the middle of the A and B series. The height-to-width ratio of all of them is the square root of two.

Despite the fact that these are the ISO standard’s basic formats, various sizes are used for printed things such as labels, business cards, and so on. They’re frequently made by slicing conventional sizes into equal pieces. This frequently results in sizes that do not have a square root of two aspect ratio.

Enlargement and Reduction Made Simple

Many copy machines include preset magnification factors for expanding or shrinking a copied document so that it may be printed on a different size of paper. These settings are usually represented by buttons labelled ‘A3 to A4’ and so on. This saves you time and prevents you from wasting margins by guessing the proper magnification factor, which might result in a stack of wasted paper.

A Perfect Match for Any Envelope

The ISO papers’ fixed aspect ratio makes it simple to fit bigger paper sizes into smaller envelopes. This may be accomplished by simply folding the larger papers in half (crease parallel to the shorter sides) until the appropriate size is achieved. The amount of times you should fold it is equal to the difference in page sizes. You should fold a piece of A2 paper in half twice if you have a C4 or B4 envelope. The same procedure may be used to file bigger paper sizes in smaller file folders.

This is compatible with B and C envelope formats. The DL format is another widely used format. An A4 sheet folded in thirds or an A5 sheet folded in half lengthwise will fit in a DL size envelope.

North American Sizes

The paper sizes used in North America are classic formats with variable aspect ratios. The Letter (8.5 x 11 inches), Legal (8.5 x 11 inches), and Tabloid (11 x 17 inches) formats are the most popular conventional sizes. You almost certainly utilise these formats on a daily basis. For corporate and academic publications, the letter is the standard. Legal pads are printed in the Legal format, whereas tabloids and smaller newspapers are printed in the Tabloid format. The origins of traditional American paper forms are little understood.

There have been a few initiatives in the United States to standardise the paper business. President Herbert Hoover established the Government size by ordering that all government papers and paperwork be printed on 8 x 10 1/2 inch paper. Because this style did not catch on with the general public, President Ronald Reagan reinstated the Letter format as the standard.

The ANSI/ASME Y14.1 standard was adopted by the American National Standards Institute in 1995. ANSI followed by a letter denotes the many forms of this system. Despite the existence of this standard, conventional sizes are still the most often utilised.

This standard is based on the classic Letter format and is still relatively new (ANSI A). Although the Letter format is similar to the ISO A4 format in terms of being extensively used for commercial and academic purposes, the sizes differ.

The ANSI paper formats are identical to the ISO paper formats in that cutting a sheet in half yields two sheets of the next size. Both the size and the aspect ratio are different. The aspect ratio of the ANSI sizes varies from 1.2941 and 1.5455. This makes it more difficult and less methodical to enlarge and reduce a page to match various ANSI formats than it is with ISO layouts. You’ll almost certainly end up with margins that aren’t the same as the source page.

The usage of American paper sizes has grown less popular in colleges, where students are increasingly commonly held to international standards while attending conferences or submitting works to international publications, causing several complications in the international interchange of documents. Fortunately, documents may be formatted to print on both ANSI and ISO paper.

Printing A4 Documents on Letter Paper and the Other Way Around

You’ve just received a document in A4 format from a German business partner that you need to print. When you print the document, you find that chunks of the top and bottom of each page have been chopped off. The difference in size between the A4 and Letter (ANSI A) formats is the reason behind this. Because the Letter format is 6 percent shorter than A4, you need set the magnification factor to 94 percent when printing or copying an A4 document on Letter. Because A4 is 3 percent narrower than Letter, you need set the magnification factor to 97 percent when printing a Letter document on it.

Something to Consider

The sort of paper you use is mostly determined by your actual location. Some persons should have both ISO and ANSI paper on hand at all times. University students and individuals who conduct foreign business or frequently send letters abroad are examples of such persons. Many local office supply businesses, regardless of nation, stock both types of paper, but special orders may be necessary.