Printer Paper Size Mismatch – Fixed in 3 Steps

Quick Fix (30 seconds) – Check the Paper Tray

I know you probably already looked. But do it again. Pull out the paper tray completely and check the paper size guides. They need to be snug against the paper. Not loose. Not jammed sideways. Snug.

Had a client last month whose HP LaserJet kept saying “paper size mismatch” every time they tried to print a label. The paper guide was shifted two millimeters to the right. Two millimeters. That’s it.

Also look at the little plastic lever or switch that tells the printer what size paper is loaded – usually on the tray itself. Make sure it matches the paper you actually put in. If it says “Letter” but you loaded A4, that’s your problem right there. Move the switch to A4 (or vice versa).

Reseat the tray firmly. Try printing again. If it works, you’re done. If not, move to the next step.

Moderate Fix (5 minutes) – Check Printer Settings on Your Computer

This is where the mismatch actually lives half the time. The computer tells the printer one thing, but the tray has something else. The printer then throws a fit.

Step 1: Check the print job settings

1. Open the document you want to print.
2. Go to File > Print (or press Ctrl+P on Windows, Cmd+P on Mac).
3. Click “Properties” or “Printer Properties” next to your printer name.
4. Find the Paper/Quality tab (or whatever your printer driver calls it).
5. Look for Paper Size. Set it to the exact size in the tray. If you loaded Letter, choose Letter. If you loaded A4, choose A4. Don’t guess. Match it.

Also check “Paper Source” or “Tray Selection.” Make sure it points to the tray you actually loaded. Some printers let you choose “Automatically Select” which works fine – but if you set it to Tray 2 and that tray has different paper, you’ll get the error.

Click OK and print. If it works now, the issue was just a mismatched print job. If not, go to step 2.

Step 2: Check default printer settings

Sometimes the default settings in Windows override the per-job settings. Here’s how to check:

1. Open Control Panel > Devices and Printers (Windows 10/11 type “Printers” in the start menu).
2. Right-click your printer and choose “Printer Properties” (not “Printing Preferences”).
3. Click the “Advanced” tab.
4. Click “Printing Defaults” button.
5. Same drill – set the paper size and tray to match what’s loaded.

I had a Brother printer at a small office where the defaults were stuck on “Letter” but they only used A4. Every print job from every computer triggered the mismatch. Fixed in two minutes by changing that one setting.

Advanced Fix (15+ minutes) – Update Firmware and Driver

If the error is still there after checking the tray and settings, it’s likely a bug in the printer firmware or driver. This happens more than you’d think.

Step 1: Update printer firmware

Go to your printer manufacturer’s support site. Find your exact model. Download the latest firmware. Follow their instructions to install it – usually you put it on a USB drive and plug it into the printer, or upload it via the printer’s web interface.

Firmware updates fix weird sensor logic. One HP OfficeJet I dealt with kept reading the paper guide as “envelope” because of a known bug in the 2022 firmware. The 2023 firmware fixed it.

Step 2: Reinstall the printer driver

Outdated or corrupted drivers love to send wrong paper size info to the printer. Do this:

1. Open Control Panel > Devices and Printers.
2. Right-click your printer and choose “Remove device.”
3. Unplug the printer (USB) or disconnect it from the network.
4. Restart your computer.
5. Go to the manufacturer’s site and download the latest full driver package (not the basic one Windows auto-installs).
6. Run the installer. When it asks, plug in the printer or connect it.
7. Let the driver install completely.

I’ve seen this fix errors that looked like hardware failures. The driver was just sending a “Letter” command even when the tray was set to A4. After a clean install, everything lined up.

Step 3 (if still not fixed) – Check the paper size sensor

This is rare, but sometimes the sensor inside the tray that detects paper size gets dirty or misaligned. Open the tray, look for a little plastic tab or optical sensor near the back or side. Clean it with a dry cotton swab. If it’s physically broken, you might need a new tray or a service call.

But honestly, 95% of mismatch errors are fixed in the first two steps. Don’t overthink it.

Pro tip: If you print from different apps (Word, PDF, web browser), each app can have its own page size setting. Check that too. I once spent 20 minutes on a guy’s printer only to realize his browser defaulted to “Tabloid” because he printed a spreadsheet earlier.

That’s it. Quick check, setting fix, driver flush. You should be printing again without that annoying error message.