Why Your QR Code Is Not Scanning: 9 Causes and Fixes
A checklist for diagnosing a QR code that will not scan, ordered from the most common cause to the most obscure.
A code that will not scan is almost always failing for a boring, mechanical reason. Work down this list in order; the fix is usually in the first three.
1. It is too small for the distance
The most common cause by far. The code needs to be roughly one tenth as wide as the distance it will be scanned from. A 2 cm code on a poster people stand a metre away from cannot work, no matter how good the phone is.
2. The contrast is too low
Light grey on white, or two similar brand tones, will fail under anything but perfect lighting. Dark modules on a light background, with real separation between the two.
3. The quiet zone has been cropped
Designers tighten margins by instinct. Scanners need at least four modules of blank space on every side to find the code's edges. If text or a border touches the pattern, restore the margin and try again.
4. It is printed on a glossy surface
Gloss reflects light straight back into the camera and wipes out part of the pattern. The same file on matte stock often scans first time. If gloss is unavoidable, size the code up and keep it away from where a spotlight will hit it.
5. The colours are inverted
Light modules on a dark background decode on some scanners and not others, because inversion handling is optional in many implementations. It looks striking and it halves your success rate.
6. There is too much data in the code
A long URL with tracking parameters produces a dense grid of tiny modules that needs a bigger print size to stay readable. Shorten the destination (a redirect link is far shorter than a URL carrying five UTM parameters) and the pattern opens up immediately.
7. The logo is too large
A centre logo covering much more than 20% of the area overruns even level H error correction. Shrink the logo, or accept a larger code.
8. The code is physically damaged
Scuffs, folds through a finder pattern, condensation, or fading from UV exposure all remove data. Anything living outdoors or getting handled should be printed at level Q or H, laminated where possible, and checked periodically.
9. The code scans, but the destination is dead
Worth confirming before reprinting anything: the camera recognises the code and offers a link, but the page 404s or the site has moved. This is the argument for tracking links: the printed code stays the same and the destination behind it can be corrected without a reprint.
Roughly nine in ten scan failures are one of the first three items above: size, contrast, or a cropped quiet zone. Rule those out before chasing anything more exotic.
How to test properly
Scan the physical copy, at final size, on the final material, with at least two phones (one recent, one a few years old) under the lighting the code will actually live in. On-screen tests prove nothing about a printed code, because a backlit screen flatters the pattern in a way paper never does.
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