Glossary
Module
A module is one square cell of a QR code — the smallest unit of the pattern. Codes are measured in modules, not pixels or millimetres, because the module count is fixed by the version and the physical size is whatever you print it at.
Why modules matter more than pixels
Every scanning rule is really a rule about modules. A camera needs roughly 2–3 pixels per module to decode reliably, and a printer needs the module to survive ink spread. So the two questions that decide whether a code works are: how many modules does my payload need, and how many millimetres will each one be?
| Version | Modules across | At 0.5 mm/module | At 1 mm/module |
|---|---|---|---|
| 1 | 21 | 10.5 mm | 21 mm |
| 5 | 37 | 18.5 mm | 37 mm |
| 10 | 57 | 28.5 mm | 57 mm |
| 20 | 97 | 48.5 mm | 97 mm |
| 40 | 177 | 88.5 mm | 177 mm |
A practical floor for consumer printing is 0.4 mm per module; below that, ink spread and camera resolution start eating the pattern. See size for print.
Related
- Quiet zone — The quiet zone is the blank margin around a QR code. The specification requires at least four modules of clear space on every side, and codes fail more…
- Version — A QR code's version is its size: version 1 is 21 × 21 modules and each step adds 4 modules per side, up to version 40 at 177 × 177. The encoder picks the…
- Data capacity — Data capacity is how much a QR code can hold, and it depends on three things at once: the version, the error-correction level and the encoding mode. The…