QR code · One dark or light square
QR module size
How large each square must be printed for a camera to resolve it.
Key facts
| Module | One dark or light square |
|---|---|
| Symbol width | modules × module size + 8 modules of quiet zone |
| Practical floor | About 0.3–0.4 mm per module for close-range print |
| Screen rule | At least 2–3 device pixels per module |
| Scan distance | Roughly 10× symbol width for phone cameras |
| Non-uniform scaling | Breaks decoding |
Print size follows module count
A 21×21 symbol printed at 0.5 mm per module is 10.5 mm wide plus margins. The same payload at a higher version may be 33×33 modules and need 16.5 mm for the same module size. This is why shortening the payload is often the only way to keep a physical label small and scannable.
Screens are different
On a display, the limit is resolution, not ink spread. Render with nearest-neighbor scaling and give each module at least two or three device pixels. Blurred edges from CSS scaling or image smoothing are a common cause of codes that look sharp to a person but fail to scan.
Frequently asked questions
What is the smallest scannable QR code?
It depends on the camera and the module count. For phone scanning, keep the printed symbol at least about 2 cm wide with a 4-module quiet zone.
Does error correction help with tiny modules?
Only after the camera resolves the modules. If adjacent modules blur together, no correction level can recover the pattern.
Can I stretch a QR code to fit a rectangle?
No. Non-uniform scaling changes module geometry and breaks the finder-pattern ratios.