A4 vs US Letter: the paper sizes, and how to convert between them
The exact sizes of A4, US Letter, Legal and the A series, which countries use which, why documents print badly on the other size, and how to convert a PDF.
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Tools for this job: PDF Page Size Converter · Multiple PDF Pages Per Sheet · PDF Booklet Maker
Most of the world prints on A4. The United States and Canada print on US Letter. The two look almost identical, which is exactly why they cause trouble: a document made for one usually prints on the other with a margin cut off or a strip of empty space, and nobody notices until it comes out of the printer.
The sizes
| Size | Millimetres | Inches |
|---|---|---|
| A4 | 210 × 297 | 8.27 × 11.69 |
| US Letter | 215.9 × 279.4 | 8.5 × 11 |
| US Legal | 215.9 × 355.6 | 8.5 × 14 |
| A3 | 297 × 420 | 11.69 × 16.54 |
| A5 | 148 × 210 | 5.83 × 8.27 |
Letter is 5.9 mm wider than A4 and 17.6 mm shorter. A4 is the narrower, taller sheet.
Who uses which
US Letter and Legal are standard in the United States and Canada, and common in parts of Latin America and the Philippines. Almost everywhere else uses the international A series, defined in the ISO 216 standard, with A4 for everyday documents. If you send documents across that line — a CV to a company abroad, a report to an overseas client, forms to a foreign government office — paper size is worth a moment's thought.
Why the A series is so tidy
Every A size has sides in the ratio 1 to the square root of 2. That ratio has a useful property: cut a sheet in half across its long side and both halves have the same shape as the original. So A3 folded in half is two A4 pages, A4 folded in half is two A5 pages, and a photocopier can enlarge A4 to A3 or shrink it to A5 without leaving margins. The largest size, A0, has an area of exactly one square metre. US paper sizes have no such relationship, which is why enlarging Letter to its larger counterparts always changes the shape.
What goes wrong when you print on the wrong size
- A4 document on Letter paper: the page is about 18 mm too tall. Printed at actual size, the bottom margin — often a footer or page number — is cut off. Printed with “fit to page”, the whole page shrinks to about 94% with wider side margins.
- Letter document on A4 paper: the page is about 6 mm too wide. Printed at actual size, the right edge can be clipped; scaled to fit, it shrinks slightly and gains extra space at the top and bottom.
Neither is disastrous for a letter, but it matters for forms that will be scanned, labels, anything with content near the edges, and documents where page numbers must appear.
Converting a PDF to the other size
- Add the file to the PDF Page Size Converter. Its current page sizes are listed.
- Choose the target paper — A4, US Letter, US Legal, A3 or A5.
- Choose Scale to fit to shrink or enlarge the content so it fits the new paper without anything being cut off, or Keep content size to change only the paper around it.
- Convert, check the sizes read back from the saved file, and download.
Scale to fit uses the largest factor that fits both dimensions. From A4 to Letter that is 94.1%, leaving a little extra space at the sides. From Letter to A4 it is 97.3%, leaving extra space at the top and bottom. The content is scaled as drawing instructions rather than as a picture, so text stays sharp and selectable.
Getting it right when you write the document
The cleanest fix is to set the page size before you start. In a word processor, choose the paper size in the page or layout settings at the beginning, not the end — changing it afterwards reflows every page and can move pictures and page breaks. If you do not know where a document will be printed, keep generous margins of at least 20 mm and avoid placing anything important near the bottom of the page; such a layout survives either paper size.
Microsoft Word also has an option in its advanced print settings to scale content for A4 or Letter paper automatically when the document and the printer disagree. It is handy, but it only helps when the document is printed from Word itself — a PDF you send to someone else carries the size it was made with.
Printing several pages on one sheet
For handouts and drafts, size differences matter less if you put two pages on each sheet: Multiple PDF Pages Per Sheet scales each page into a cell on the sheet and keeps the text selectable. To make a folded booklet instead, see how to print a booklet from a PDF.
Quick answers
- Is A4 bigger than Letter? It is taller but narrower. Its area is slightly larger: about 624 cm² against 603 cm².
- What is half of A4? A5, 148 × 210 mm. Half of Letter is 5.5 × 8.5 inches, sometimes called half letter or statement.
- What size are most printers set to? Whatever was standard where they were sold. Check the paper size in the print dialog whenever a document comes from abroad.