# Why QR codes fail to scan > Why QR codes fail to scan: 12 causes ranked by how often they occur, each with a fix, plus a four-step routine for diagnosing a code that will not read. Source: https://qr-code-build.com/learn/why-qr-codes-fail-to-scan/ Last reviewed: 2026-08-24 Publisher: QR Code Builder ## Summary The most common causes of QR code scan failure are, in order: too small for the scanning distance, a missing or cropped quiet zone, insufficient contrast between modules and background, and reflective glare from gloss finishes. All four are print and design problems rather than phone problems. ## Twelve causes, most frequent first 1. **Too small.** Below roughly 0.4 mm per module, phones struggle. Fix: enlarge, or shorten the payload so the code has fewer modules. 2. **Quiet zone cropped.** Four modules of clear space on every side are required. Designers trim this constantly. Fix: restore it; it is part of the artwork. 3. **Poor contrast.** Mid-tone modules on a mid-tone background, or a light-on-dark inversion. Fix: dark modules on a light background, checked in greyscale. 4. **Glare.** Gloss lamination, spot UV or glass reflecting light into the lens. Fix: matte finish; reposition away from direct light. 5. **Blur.** A low-resolution image scaled up, or a code placed too close for the camera to focus. Fix: vector artwork, and a minimum focus distance of about 10 cm. 6. **Damage over a finder pattern.** Error correction does not protect the corner squares. Fix: reprint; there is no recovery. 7. **Curved or flexible surface.** Bottles, tubes, shrink sleeves. Fix: move to a flat panel, or increase size and error correction. 8. **Ink spread.** Absorbent stock thickens dark modules until light gaps close. Fix: print 10–15% larger; ask the printer for their dot gain figure. 9. **Inverted colours.** Light modules on a dark background. Permitted by the specification, refused by many older scanners. Fix: invert back. 10. **Logo too large.** Coverage beyond the error correction headroom, or placed off-centre. Fix: under 25% at level H, centred. 11. **Extreme angle.** Beyond about 30 degrees, alignment patterns cannot fully correct the distortion. Fix: reposition at eye level and face-on. 12. **The link is dead.** The code scans perfectly and the destination 404s. Fix: check the destination separately — this is not a code problem, and it is more common than any of the above once codes are in the wild. ## Isolating the cause in four steps 1. **Decode the file.** Upload the export to the [reader](/qr-code-scanner/). If it decodes on screen, the pattern is valid and the problem is physical — size, contrast, print or lighting. 2. **Scan the screen.** Display the code on a monitor and scan it from a phone. Works on screen but not in print? Print quality, size or finish. 3. **Try two phones.** One recent, one budget. If only the budget phone fails, the code is marginal rather than broken — enlarge it. 4. **Change the light.** Take the printed piece to a window. If it suddenly scans, the cause is glare or dim lighting, not the code. ## A pre-print checklist - Decode the final export file and confirm the payload is exactly right, character for character. - Print a proof at final size on the final stock, and scan it with two phones. - Check the quiet zone survived the layout application. - Confirm the finish is matte over the code area. - Open the destination on mobile data with a cleared cache. - Look at the code in greyscale to confirm contrast. - For runs over a few hundred, scan a unit from the actual production run, not just the proof. ## Frequently asked questions ### Why does my QR code work on screen but not in print? Almost always size, contrast or finish. Screens are backlit and high contrast; paper is neither. Check module size and use a matte finish. ### Why do some phones scan my code and others do not? The code is marginal rather than broken. Camera quality and decoder implementations vary; enlarge the code or raise the contrast to build margin. ### Can a damaged QR code be repaired? Error correction repairs damage up to its level automatically, unless the damage covers a corner finder pattern, in which case the code cannot be located at all. ### What is the most common reason QR codes fail? Printing them too small for the distance they are scanned from, followed closely by cropping the quiet zone. --- Licence: this page may be quoted with attribution to QR Code Builder (https://qr-code-build.com/learn/why-qr-codes-fail-to-scan/).