Decoding the Matrix: How QR Code Technology Really Works | how qr codes work

A QR code can store up to 7,089 numeric characters, 4,296 alphanumeric characters, or 2,953 binary bytes. This high density is achieved through four standardized encoding modes and the use of Reed-Solomon error correction, which allows the code to be read even if it is partially obscured or damaged.

QR codes feature four Reed-Solomon error correction levels: Level L (7% recovery), Level M (15%), Level Q (25%), and Level H (30%). Higher levels of error correction increase the number of redundant modules, making the code more robust against damage but reducing the total amount of user data that can be stored in the same physical space.

The three large squares at the corners are finder patterns that help scanners identify the code's orientation and size. As codes get larger (Version 2 and above), they also include alignment patterns—smaller squares that help the scanner compensate for moderate distortion or curvature of the surface the code is printed on.

There are 40 standard versions of QR codes. Version 1 is the smallest at 21x21 modules. Each version increase adds 4 modules per side, culminating in Version 40, which consists of 177x177 modules. The more modules a version has, the higher its data capacity and the more complex its internal structure becomes.

Static QR codes encode the actual data directly into the module pattern, making them permanent. Dynamic QR codes encode a redirect URL pointing to a central server. This allows the destination data to be modified without regenerating the code and enables the collection of analytics, such as time, location, and device type of the scan.