The 10:1 rule of thumb
A widely used rule of thumb is that a QR code should be at least one tenth as wide as the distance it will be scanned from. A code read from 1 meter away should be about 10 cm wide, and a poster read from 5 meters should be about 50 cm wide. It is a starting point, not a guarantee, because lighting, camera quality and code density all shift the real limit.
- Scanned at 30 cm (1 ft): about 3 cm (1.2 in)
- Scanned at 1 m (3 ft): about 10 cm (4 in)
- Scanned at 3 m (10 ft): about 30 cm (12 in)
- Scanned at 10 m (33 ft): about 1 m (3.3 ft)
Module size matters more than overall size
What a camera actually needs to resolve is each module, the single dark or light cell. Two codes printed at the same width can scan very differently if one has 25 modules per side and the other has 57. The fewer modules a code has, the smaller it can be printed and the farther away it can be read.
Keeping the data short is the easiest way to reduce module count. A short URL, a lower error correction level where the setting allows, and no unnecessary parameters all lower the version and make each module larger.
Small print and practical floors
For close-range items such as business cards and product labels, about 2 cm (0.8 in) is a commonly cited minimum for a short URL. Denser codes need more room, and very small prints also depend on the printer’s resolution and the paper. Always leave the quiet zone of four modules on every side, which is in addition to the code’s own width.
The only reliable check is a test print scanned with several phones at the real distance and in the real light. Test on an older phone as well as a new one.