Paper sizes: A4, Letter and more: what it is and what it is for

1What paper sizes exist and how do they differ?

The two main systems are the international ISO 216, with the A series, and the North American one, with Letter, Legal and Tabloid. In the A series, A0 has an area of one square meter and each following size is obtained by folding the previous one in half: two A5 sheets make an A4, and two A4 make an A3. They all keep the same proportion, which makes it easy to enlarge and reduce without cropping.

North American sizes don't follow that logic. Letter is 8.5 × 11 inches, Legal 8.5 × 14 and Tabloid 11 × 17. In Latin America both worlds coexist, and the usual standard depends on the country and local custom, so it pays to confirm what your process or print shop asks for.

2A4 vs Letter: practical differences

A4 is a little narrower and taller than Letter: 210 by 297 millimeters versus about 216 by 279. The difference seems small, but when you print a document designed for one on the other you get different margins, text cut off at the edge or empty strips.

In the digital world a PDF stores its page size in units called points: a Letter page is 612 × 792 points, and an A4 is about 595 × 842. Many documents have that size fixed when exported, and it determines how they will look on the printer.

A curious detail of the A series is its ratio: the relation between the long side and the short side is approximately 1.414, the square root of two. Thanks to it, folding a sheet in half keeps its shape, and that's why photocopiers can enlarge from A4 to A3 without cropping anything.

• A4: 210 × 297 mm, taller and narrower.
• Letter: 8.5 × 11 in, wider and shorter.
• Legal: 8.5 × 14 in, longer than both.
• Typical safety margin: leave at least a few millimeters free.

3How to choose the right size

The simple rule: use the size requested by whoever will receive or print the document. For official paperwork, ask or check the requirements; for personal use, whatever your printer has. If the destination is screen only, size matters less, but it's best to stick to a standard one so it prints well if someone decides to print it.

When you merge PDFs from different sources you may end up with mixed page sizes. It's not an error: PDF allows pages of different sizes in the same file. But when printing it can be awkward, and it's better to standardize them first.

4Common printing problems and how to fix them

The most common symptom is content coming out cropped or with huge margins. It's almost always fixed in the print dialog: choose the fit-to-page option or the actual size option depending on what you need, and check that the selected paper matches what is loaded in the tray.

Another case is scans and photos converted to PDF, which take the size of the image and not that of the paper. If you print without adjusting, the photo may come out tiny or overflow. Cropping the margins beforehand, or a conversion that places the image on a standard page, avoids the problem.

5Myths and common mistakes

A common mistake is believing that A4 and Letter are the same and that the printer always adapts them well. Not always: some printers scale, others crop. Another is measuring a PDF on screen: the real size is defined by the document, not by the zoom you view it at.

People also think that changing the paper size in a word processor preserves the layout. In reality the text reflows and the page count can change. If the layout is critical, export again from the original program with the correct size.

6Page sizes with Rayo PDF GO

With Crop PDF you can remove excess margins from a page to fit it better to the content. With Images to PDF you convert photos or scans into a document, and with Rotate PDF you fix pages that came out sideways. Merge PDF lets you combine files into one.

Rayo PDF GO does not promise to convert every page to a standardized paper size with one click; if you need that exact result, check the size when exporting from the source. All the work is done on your device.