Work out how large a QR code has to be printed to actually scan.
The length of the URL or text. Shorter payloads make larger, more readable modules.
200 mm code for scanning at 2 m
Two things sink more printed QR codes than size does. The quiet zone is the first: four modules of blank space on every side is part of the specification, and a code printed hard against a border or a coloured background often will not scan at all. The second is payload length, since every extra character adds modules and each module gets smaller at a fixed physical size. Shortening the URL, using a redirect, and keeping error correction at M rather than H all buy back readable module size. Print a test at final size and scan it from the real distance before ordering anything.
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QR Size & Scan Distance Calculator on RunTheTests — free browser-based qr tools, no sign-up.