Why printed QR codes fail (and how to make sure yours do not)

Almost every failed QR code fails for one of four reasons, and all four are decided before printing.

1. Contrast, not colour

Scanners read the difference in brightness between the modules and the background. Dark code on a light background is the reliable arrangement. Inverted codes (light on dark) work on some phones and fail on others — treat them as decoration, not as the only way to reach you. And never place a code over a photo or gradient: the scanner needs a flat field.

2. Physical size, measured from where people stand

A rough rule that works: the minimum printed width in centimetres is about half the scanning distance in metres. A code read from 2 m should be at least 10 cm across; on a table tent read at 30 cm, 4 cm is fine. Below about 2 cm, most phone cameras start struggling.

3. The quiet zone

The empty margin around the code is part of the specification, not padding. Designers love cropping it. That single edit is the most common cause of a code that worked on screen and fails on paper. Keep at least four modules of clear space on every side, and do not let a border or text creep into it.

4. Where it lives

Flat surfaces, good light, no glare. Not wrapped around a curve, not behind reflective plastic, not on a window that catches sun. On a menu, put the code at the top of the page rather than half under someone's thumb.

Always proof it

Print one, at final size, on the actual material, and scan it with two different phones. A proof costs a few cents; a print run with a dead code costs the run.

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