The two sizes in numbers
A4 measures 210 x 297 mm (about 8.27 x 11.69 in). US Letter measures 8.5 x 11 in, which is 215.9 x 279.4 mm. Letter is slightly wider and noticeably shorter. A4 is narrower and taller.
| Size | Millimeters | Inches |
|---|---|---|
| A4 | 210 x 297 | 8.27 x 11.69 |
| Letter | 215.9 x 279.4 | 8.5 x 11 |
The difference is only a few millimeters in width and about 17.6 mm in height. That small gap is enough to cause real problems when a document built for one size is printed on the other.
Where each size is used
Letter is the standard office size in the United States and Canada, and it is common in a few other places. A4 is the standard in most of the rest of the world. If you are not sure which one your printer is loaded with, check the label on the paper tray or the paper ream wrapper.
What goes wrong when the sizes do not match
Printing an A4 file on Letter paper, or the other way around, usually ends in one of three results.
- Scaling. The printer or driver shrinks or enlarges the page to fit. Everything is complete, but nothing is its true size. A 100 mm line can end up around 94 mm when an A4 page is fit onto Letter.
- Clipping. The page prints at its true size but the paper is shorter or narrower than the file. The edges are cut off, often the footer or the right margin.
- Extra margins. The page is centered on a larger sheet and looks small, with wide white borders.
Which result you get depends on the app, the print dialog, and the printer driver. The fix is the same in every case: make the document size, the paper size setting, and the paper in the tray all agree.
Actual size versus Fit
Most print dialogs, including the PDF viewer’s dialog, offer a scaling option. Names vary by app, but two ideas appear almost everywhere.
- Actual size (sometimes called 100% or None) prints the page at its true dimensions. Use this for anything where measurements matter, such as a test page, a template, a sewing pattern, or a technical drawing.
- Fit (sometimes Fit to page or Shrink to fit) rescales the page so it fits inside the printable area. This is convenient for ordinary documents but changes the real size.
Even Actual size can clip content that sits very close to the paper edge, because most printers cannot print all the way to the edge. Keeping important content inside a margin of a few millimeters avoids this.
How to check that a print is the right size
The quickest test is to print something with a known length and measure it with a ruler. Our scale check sheet has a 100 mm bar, a 4 in bar on the Letter version, and a bank-card-size box. Print it with scaling set to Actual size, then measure. If the bar is not 100 mm, the print was scaled, and you can use the tool to see by how much. If you want to see where the printer’s margins fall, the alignment and margins page has nested frames that show which edges are cut off.
If the result is wrong, prints come out too small walks through the usual causes.
Choosing the right file
Where you can, pick the file that matches your paper. Every PDF on this site comes in both versions, and the download hub lists them side by side. If you only have the other size, print at Actual size and expect some trimming at the edges, or use Fit and accept that measurements will be off by a few percent.
Changing the default paper size
Many printers and operating systems default to the size common in your region. If prints keep coming out scaled, look at the default paper size in the printer’s preferences and in the app you are printing from. The steps differ by system, so see the how-to guides for Windows, Mac, iPhone and iPad, Android and Chromebook.
Quick checklist
- Confirm which paper is in the tray.
- Choose the same size in the print dialog.
- Choose Actual size (or 100%) when measurements matter.
- Print the scale check sheet and measure the 100 mm bar.
- If the result is off, check the printer driver’s paper size too, since it can override the app.