Direct answer
On the covered Brother printer, Size Mismatch, Size Error DX, Wrong Paper Size means the paper in the tray is not the correct size — Brother's own wording for Size Mismatch. Brother uses Size Error DX for the two-sided case, where the size set in the printer driver is not one the machine can duplex; inkjet models word the same condition as Wrong Paper Size. First, compare tray guides, paper and print settings.
Definition versus diagnosis
The display names a detected condition—not an automatically failed part.
What this covers
- Brother printer covered by the cited source
- Displayed code or documented alias: Size Mismatch, Size Error DX, Wrong Paper Size
- The exact operating state described by the manufacturer
What it does not cover
- ×Another product type or original-manufacturer platform
- ×A visually similar but different code
- ×Internal live electrical, sealed-system, gas, battery-cell or control-board repair
Match every character and the exact product
ReversiblePhotograph the complete display and product label. This record covers Size Mismatch, Size Error DX, Wrong Paper Size on Brother inkjet and laser printers/MFC devices; displayed wording and error numbers vary by engine and supply system.
Preserve the failure state
ReversibleCompare tray guides, paper and print settings. Record the operating stage, recent change and what still works before clearing the message.
Correct only the documented fault domain
ReversibleMake all three use the same supported size. Do not borrow a reset or meaning from a similar code, product or model year.
Verify once, then respect the service boundary
ReversibleRepeat only the shortest safe action that reaches the original stage. If Size Mismatch, Size Error DX, Wrong Paper Size returns, stop repeated resets and use model-specific manufacturer support.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Exact questions
Common follow-ups
What does Size Mismatch, Size Error DX, Wrong Paper Size mean on a Brother printer?+
the paper in the tray is not the correct size — Brother's own wording for Size Mismatch. Brother uses Size Error DX for the two-sided case, where the size set in the printer driver is not one the machine can duplex; inkjet models word the same condition as Wrong Paper Size.
Can I reset Size Mismatch, Size Error DX, Wrong Paper Size without fixing the cause?+
A reset may hide the display temporarily but does not correct the documented fault. Record the code and complete only the safe checks first.
Why is the complete model number required?+
Manufacturers reuse characters across platforms. The model number determines which official table, controls and service boundary apply.
When should I stop?+
Stop for smoke, arcing, burning odor, uncontrolled water, gas odor, battery swelling, extreme heat or any condition the manufacturer directs to professional service.
Answer for the exact device and software version shown above.