What the standard covers
ISO/IEC 24778 specifies the Aztec code: the central bullseye finder, the orientation marks, the reference grid, the layers of data that spiral outward, and the Reed–Solomon error correction. It also includes the reference decoding algorithm.
The Aztec code was invented by Andrew Longacre Jr. at Welch Allyn in the mid-1990s and was published as an AIM specification before becoming an ISO standard in 2008. A second edition was published in 2024.
Sizes and capacity
Aztec codes come in compact forms with 1 to 4 layers and full-range forms with 1 to 32 layers. The smallest compact symbol is 15 × 15 modules and the largest full-range symbol is 151 × 151 modules.
The largest symbol holds up to 3,832 digits, 3,067 alphabetic characters or 1,914 bytes. The share of error correction is chosen by the encoder, with about 23 percent often recommended as a default.
- Compact: 1–4 layers, 15 × 15 to 27 × 27 modules
- Full-range: 1–32 layers, 19 × 19 to 151 × 151 modules
- Largest capacity: 3,832 digits or 1,914 bytes
- No quiet zone required
Where it is used
Because the finder is in the middle, an Aztec code needs no quiet zone and can be printed right up to the edge of a label or shown full screen on a phone. It is common on transport tickets, including many rail tickets and mobile boarding passes.