What is a QR code and how is it generated?

Short answer
A QR code (Quick Response code) is a two-dimensional barcode that stores data - most commonly a URL - in a matrix of black and white squares. Smartphone cameras read QR codes instantly without a separate app on modern iOS and Android devices. They are generated algorithmically: the data is encoded using Reed-Solomon error correction, then mapped into the square grid pattern at one of four error correction levels (L, M, Q, H).

QR codes were invented in 1994 by Denso Wave, a Toyota subsidiary, to track vehicle parts during manufacturing. The format was designed to be read ten times faster than a standard barcode (hence 'Quick Response'). The patent holder made the technology royalty-free, which is why QR codes proliferated freely across industries.

The data capacity of a QR code depends on the version (size) and error correction level chosen. Version 1 is a 21x21 grid capable of storing 41 numeric characters. Version 40 is a 177x177 grid capable of storing 7,089 numeric characters or 4,296 alphanumeric characters. URLs are encoded as byte data, with a typical short URL requiring a small version-2 or version-3 code.

Error correction is what makes QR codes scannable even when partially damaged or obscured. Level L corrects up to 7% damaged codewords, Level M corrects 15%, Level Q corrects 25%, and Level H corrects 30%. Higher correction levels produce denser (harder to scan at small sizes) but more resilient codes. Branded QR codes with logos in the centre use Level H error correction because the logo intentionally obscures part of the code.

For marketing applications, always link a QR code to a UTM-tagged URL rather than a bare destination URL. This lets you attribute scans to specific campaigns and physical placements in your analytics dashboard. Also test every generated QR code with at least two different devices before printing, as minor rendering issues can make a code unscannable at small print sizes.

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