Capacity is measured by encoding mode and bytes
There is no single character limit that applies to every message. QR capacity depends on the QR version, error-correction level, and encoding mode. At the largest standard QR version and the lowest error correction, the specification allows up to 4,296 alphanumeric characters or 2,953 bytes in byte mode. A practical code may hold much less because higher error correction, Unicode, emoji, and design choices consume capacity or increase density.
Treat the generator preview as a technical check, not proof of real-world readability. Shorten the message or move long content to a web page when the modules become too dense for the intended print size.