A paper size mismatch error means the printer was told to expect one size and is set for, or detects, another. Three things must agree: the page size in your document, the paper size in the driver, and the size the printer believes is in the tray. When any one differs, the printer stops and asks for paper, or prints with parts cut off. The most common mix-up is between A4 and Letter. This guide shows where each setting lives and how to make them match.
What you might be seeing
- The control panel asks for a paper size that is not loaded
- Printing pauses until you press OK or feed paper manually
- The page prints but is cropped or shrunk
- The error appears only from one app or one device
Common causes
- Document size differs from the paper
- Templates, downloads and files from other countries often default to A4 or Letter.
- Driver default set wrong
- The driver may default to a different size, especially after a reinstall.
- Outdated tray setting
- The size stored for the tray may not match what you loaded.
- Guide-based size detection
- Some trays sense size from the guide positions, so a misplaced guide reports the wrong size.
How to fix it, step by step
Work through these in order and test a print after each one. Most people are done within the first few steps.
Read what the printer is asking for
Look at the exact message on the control panel or in the print queue. It usually names the size the job requested and sometimes the tray it expected. That tells you which side to fix: if it asks for A4 while Letter is loaded, the document or driver is set to A4. Cancel the job before changing settings so the printer stops waiting for it.
Set the page size in the document
Check the page setup in the app you are printing from. In Microsoft Word, use Layout › Size; many other programs use File › Page Setup. On a Mac, File › Page Setup has a Paper Size menu, and the print dialog has its own. Choose the size you actually loaded. For a PDF you cannot edit, choose your paper in the print dialog and enable a fit option.
Change the driver's default paper size
On Windows 11, go to Settings › Bluetooth & devices › Printers & scanners, click your printer and open Printing preferences. On Windows 10, the path is Settings › Devices › Printers & scanners, then your printer, Manage and Printing preferences. Set Paper Size to your usual size and select Apply. New jobs that do not specify a size will now follow it.
Update the tray size on the printer
On the control panel, open the paper or tray settings and set the size for the tray you loaded. Many printers ask you to confirm size and type each time a tray closes; if that prompt was skipped, the old values remain. On trays that read the guide positions, push the guides fully against the paper so the tray reports the correct size.
Check Mac and mobile defaults
On a Mac, open System Settings › Printers & Scanners and set Default paper size to your usual size. On iPhone and iPad, AirPrint uses the paper size chosen in each print dialog, so check it in the print options when your printer offers a choice. On Android, the paper size sits in the print preview's dropdown, and menus vary by phone maker.
Use the A4 and Letter substitution option
If you often receive documents in the other standard size, some printers offer a setting that prints A4 jobs on Letter paper or the reverse, sometimes called A4/Letter override or paper size substitution. Look for it in the control panel's paper handling or system settings, or on the printer's web page, opened by typing its IP address into a browser. Expect slight scaling or margin differences.
Reinstall the driver if the size keeps reverting
If the default keeps changing back, the printer entry may be carrying settings from an old installation. Remove the printer from Printers & scanners, restart the computer and add it again, letting Windows Update supply the driver or installing the current one from the manufacturer's official website. Set the default paper size again before your next print job.
How to keep it from happening again
- Use the same default size in the driver, the printer and your apps
- Confirm the size prompt each time you reload a tray
- Check page setup on downloaded templates before printing
- Keep each tray loaded with a single size
Common questions
What is the difference between A4 and Letter?
Letter measures 8.5 by 11 inches and is standard in the US, Canada and a few other countries. A4 measures 210 by 297 millimeters, slightly narrower and taller, and is standard almost everywhere else. One prints acceptably on the other with scaling, but a printer set to check sizes strictly will flag the difference.
Why does the error happen only with PDFs?
A PDF carries its own page size, which overrides your driver's default. If it was created as A4, the printer receives an A4 job even when your settings say Letter. In the PDF viewer's print dialog, select your loaded paper size and turn on a fit or shrink option so the page scales to the paper.
Can I just press OK and keep printing?
Often, yes. Many printers continue on whatever paper is loaded, sometimes with clipped edges or extra white space. That is fine for a one-off page, but correcting the settings saves time and avoids cut-off content on the documents that matter most.
This guide is general information written for common home and office printers. Menus and button names vary between models, so check your printer’s manual where a step differs. Printer Problems Solved is independent and not affiliated with any printer manufacturer. See our disclaimer.