QR Code will not scan: 12 causes and how to fix each one
Date Published
When a QR Code will not scan, the cause is almost never the generator. It is one of a handful of predictable situations, and every one has a fix. This is a diagnostic route, from most likely to least likely.
First of all: test on screen
Scan the code directly from the computer screen before printing. If it reads on screen but not on paper, the problem is printing or size. If it does not read even on screen, the problem is the content or the drawing. That single test halves the diagnosis.
1. Too small
The most common cause of all. Apply the 10-to-1 rule: the side of the code should be at least a tenth of the scanning distance. Details and a full table in the print size guide.
2. Insufficient contrast
Light grey on white, yellow on beige, dark blue on black: combinations that look elegant on screen and are unreadable to a camera. The reader must clearly distinguish dark module from light background. When in doubt, print in black and white.
3. Inverted colors
A light code on a dark background fails in a meaningful share of readers, because many algorithms assume dark modules on a light background. It is aesthetically tempting and technically risky. Stick to the standard.
4. Invaded white margin
Text, frame, colored border or photo touching the code. The 4-module clear zone is part of the specification. Move everything away and the problem usually disappears.
5. Logo too large in the centre
Above roughly 30% of the area, not even high error correction recovers it. Shrink the logo, centre it and test. Details in how to add a logo without breaking scanning.
6. Textured or photographic background
Printing the code over a photograph drops the scan rate drastically, even when it looks legible. Place the code on a solid light-colored rectangle.
7. Content too long
A lot of content means many modules, smaller modules and harder scanning. It is the classic problem of a contact QR Code with every field filled in. Cut the information or increase the printed size.
8. Curved, glossy or uneven surface
Bottles, cans, plastic packaging and varnished paper distort or reflect. Position the code on the flattest, most matte area available and increase the size.
9. Poor print quality
Smudged ink, absorbent paper, a printer low on toner, or a PNG enlarged beyond its resolution. Modules merge and the reader can no longer distinguish the grid. Use SVG whenever printing.
10. Ambient lighting
Very dim light makes the camera lose contrast; strong direct light creates glare. If the code sits in a window or on a counter under a spotlight, test in the real place at the real time of day, not just at your desk.
11. An error in the content, not the code
Sometimes the code scans perfectly and it is the destination that is wrong. Typical symptoms:
- Browser opens with a page error: the URL was typed wrong or lacks "https://".
- Wi-Fi connects with an invalid password: a special character in the password or the wrong security type. See the Wi-Fi page.
- WhatsApp says the number is invalid: the country code is missing. See the WhatsApp page.
- Payment opens with a truncated name: the 25-character limit in the specification. See the PIX page.
12. The other person’s reader
Old devices, a dirty lens, a low-resolution camera, or a third-party camera app that does not recognise the format. You do not control this, but you can mitigate it: test on at least one iPhone and one Android, and always print the essential information in text next to the code.
Quick checklist
- Does it scan on the computer screen? If not, the problem is content or drawing.
- Is the code dark on a solid light background?
- Is the white margin around it clear?
- Does the size respect the 10-to-1 rule?
- Does the logo, if any, take up less than 30% of the centre?
- Is the file SVG, or PNG at 300 DPI at final size?
- Have you tested on two different devices, at the real distance and in the real light?
Working through those seven points resolves practically every scanning problem before it becomes a loss.