Minimum QR Code Size for Reliable Scanning
A practical floor for close-range scanning — something read at arm's length, like a business card or product label — is roughly 2×2 cm (about 0.8 inches) square. That minimum has to scale up with viewing distance: a common print-industry rule of thumb is that a QR code's side length should be roughly one-tenth of the intended scanning distance.
The 2 cm guideline exists because below that size, the individual modules that make up the pattern become too small for a typical phone camera to resolve cleanly at normal focus distance, especially under imperfect real-world conditions — a slightly soft printer, cheap paper stock, or a scanner held at an angle. It's not an official ISO number, it's a practical floor that print shops and designers have converged on for a code meant to be scanned close-up, like on a business card, product packaging, or a table tent.
The one-tenth rule is the more generally useful guideline because it accounts for distance directly: a code meant to be scanned from about 1 meter away should be roughly 10 cm per side; from 3 meters away, roughly 30 cm; and so on. This isn't a strict physical law, it's a rough heuristic based on typical phone camera focal length and autofocus range, but it scales sensibly and is easy to apply when planning signage, posters, or anything not scanned at arm's length. When in doubt, round up rather than down — a code that's slightly larger than necessary costs nothing; one that's too small simply won't scan.
Content matters too. A QR code encoding a short URL and one encoding a full vCard contact card are not the same size at the same physical dimensions — the vCard needs more modules to hold that data, so at an identical print size, its individual modules are smaller and harder to resolve. That means a data-heavy code needs a larger minimum print size than a lightweight one to remain reliably scannable at the same distance. If a use case calls for encoding a lot of information, either size the code up accordingly or, where possible, cut the payload down to a short link instead.
When generating a code with QRSen, it's worth deciding on the physical print size before choosing content type and error correction level, not after — sizing decisions and content decisions affect each other. The companion blog post on QR code sizing walks through this in more depth with examples across common print formats.
As a final sanity check before a large print run, print a single proof at the exact intended size on the exact intended paper stock, then test-scan it with more than one phone from the distance it will realistically be viewed at. A digital preview on a bright monitor can look perfectly scannable while the same code, shrunk onto matte paper under dim lighting, tells a different story.