The United States and Canada Are the Last Major Countries Still Using Letter-Size Paper. Here Is What Happens to Documents Crossing the Divide.
Virtually every country in the world uses A4 paper as its standard document size. The United States and Canada use Letter. These two sizes look similar: A4 is 8.27 by 11.69 inches, Letter is 8.5 by 11 inches. The difference of a quarter inch in width and two thirds of an inch in height seems trivial. In practice, that difference breaks documents constantly. An A4-formatted PDF printed on Letter paper clips the bottom. A Letter-formatted PDF printed on A4 paper clips the right margin. The two systems are close enough that the error is invisible until the document is in someone's hand with text cut off.
This is not a new problem. The ISO 216 standard that defines A4 was formalized in 1975, building on a German standard from 1922 that was itself based on Georg Christoph Lichtenberg's 1786 paper on aspect ratios. The United States established Letter as the national government standard only in the early 1980s, by which point the rest of the world had already standardized on ISO formats. The mathematical basis of ISO paper sizes, an aspect ratio of 1 to the square root of 2, means that each size in the series scales perfectly to adjacent sizes: an A4 page folded in half is exactly A5, and two A4 pages side by side are exactly A3. Letter-size paper has no such relationship.
For anyone working across national contexts, the gap between these two standards is a daily operational reality. Contracts prepared in Berlin need to print correctly in Chicago. Research reports from Canadian universities get distributed to European partners. Every time a document crosses the A4/Letter boundary, something may break. Understanding what resizing a PDF actually does to the content is the first step to crossing that boundary reliably.
The Mathematical Structure of ISO Paper Sizes
The ISO 216 system was designed with a specific property: the aspect ratio of every paper size in the system is 1:root-2, approximately 1:1.414. This ratio was chosen because it allows perfect halving: fold a sheet of paper at the short axis and the two halves are the same aspect ratio as the original. A0 is one square meter in area. A1 is half of A0. A2 is half of A1. A4 is A0 divided by 16. Every size in the series maintains the same proportions.
The practical consequence is that scaling between ISO sizes requires no content adjustment: a document designed for A4 can be printed at 50 percent on A4 to produce an A5 version with identical proportions. A4 enlarged by 141 percent fills an A3 sheet. These conversions are exact because of the square root of 2 ratio.
Letter size does not have this property. 8.5 by 11 inches has an aspect ratio of approximately 1:1.294. Two Letter pages side by side are 17 by 11 inches, which is Tabloid or ANSI B, but the aspect ratio changes. There is no clean mathematical relationship between Letter and the ISO sizes. Scaling from Letter to A4 or A4 to Letter is always an approximation.
What Breaks When a PDF Crosses the Boundary
When an A4-formatted PDF is opened on a system configured for Letter-sized printing and the user clicks print without checking settings, the result depends on the printer driver's behavior. Most print drivers default to fitting the content to the loaded paper size. If fitting is enabled, the content scales to approximately 97 percent of its original size, which is usually unnoticeable. If fitting is disabled, content extends beyond the printable area of the Letter sheet, and the bottom 0.69 inches of every page may be cut off.
The inverse problem is more visible. A Letter-formatted PDF printed on A4 paper has right and bottom margins that are slightly narrower than intended, and if the document's content extends close to the edge of the Letter canvas, it may appear too close to the paper edge or clip slightly.
Neither problem destroys a document, but both create professional presentations where the formatting is slightly off in ways that reflect badly on the sender. A legal brief prepared for a US court that is printed in London for a colleague's reference should look correct regardless of local paper settings.
When PDF Resizing Matters
PDF resizing changes the defined canvas dimensions of each page in the file. When you resize an A4 PDF to Letter dimensions, the page canvas expands from 595 by 842 points to 612 by 792 points (PDF dimensions are always in points where 72 points equal one inch). The content can either be scaled to fit the new canvas, preserving its proportions while slightly adjusting size, or left in place with the canvas adjusted around it, changing the margins.
This matters in four concrete situations. First, when preparing a document for printing in a country where the paper standard differs from where the document was created. Resizing before printing ensures the document fits the physical paper correctly regardless of printer driver settings.
Second, when submitting documents to institutions that require a specific page size. Many courts, government agencies, and journals specify A4 or Letter in their submission guidelines. Submitting the wrong size may cause rejection or require resubmission.
Third, when combining documents from multiple sources into a single PDF. If one section was created in A4 and another in Letter, the combined document has inconsistent page sizes that can cause problems in document management systems and printing workflows.
Fourth, when converting legacy documents formatted for sizes that are no longer standard, such as Legal (8.5 by 14 inches), Folio, or executive sizes. Resizing to a current standard makes them easier to print and archive.
Scaling vs. Repositioning During Resize
When resizing a PDF, there are two approaches to handling the existing content, and the right choice depends on the situation.
Scaling fits the content to the new page size proportionally. The content becomes slightly larger or smaller. Text remains readable, images remain proportional, and the overall layout is preserved. This approach is correct when the content should fill the page in the new format the same way it filled the page in the original format.
Repositioning, or no scaling, moves the content origin but does not change the size of any element. The content remains exactly as it was, and the page canvas changes around it. This adds or removes margins depending on whether the new page is larger or smaller than the original. This approach is correct when the content size must remain exactly as specified, such as for documents with legally prescribed font sizes or margins.
For A4 to Letter conversion and the reverse, the size difference is small enough that either approach works acceptably in most cases. The choice becomes more significant when converting between sizes with larger differences, such as from A3 to A4 or from Legal to Letter.
The Right Approach for International Documents
For documents that need to work in both A4 and Letter contexts, the most reliable approach is to create and distribute the document in the format required by the most critical recipient. If the document will be filed with a US court, Letter is correct. If it will be distributed primarily to European partners, A4 is correct.
For documents that genuinely need to work in both contexts without resizing, designing with slightly conservative margins, avoiding content in the outer 15mm on all sides, creates a document that prints acceptably on both sizes without visible clipping or awkward white space.
When resizing is necessary, the converted PDF should be reviewed on screen before printing to confirm content is positioned correctly within the new canvas. The slight scale change that occurs during A4-to-Letter or Letter-to-A4 conversion is invisible in most documents but can cause alignment issues in page-precise layouts like forms with printed grid lines or technical drawings with exact dimension annotations.
Conclusion
The A4 versus Letter divide is a legacy of national standards that crystallized at different times in different places and have proved too entrenched to harmonize. For most people, the gap is invisible until a document prints with the bottom clipped or a submission is rejected for the wrong page dimensions. At that point, resizing is the correct fix.
ToolHQ's Resize PDF tool handles A4-to-Letter, Letter-to-A4, and any other page size conversion securely on the server, deleting files immediately after processing, with control over whether content scales to fit or stays at its original size within the new page dimensions.
Frequently Asked Questions
Will resizing a PDF from A4 to Letter distort the content?
Not visibly. The size difference is about 3 percent in width and 6 percent in height. Scaled content adjusts proportionally and looks correct. Fonts, images, and layouts are preserved.
Which countries use A4 and which use Letter?
The United States and Canada use Letter (8.5x11 inches). Virtually every other country uses A4 (8.27x11.69 inches) under the ISO 216 standard established in 1975.
Do submission guidelines ever specify page size?
Yes. Many courts, government agencies, academic journals, and publishers specify A4 or Letter. Submitting the wrong size can result in rejection or required resubmission.