A practical character limit I recommend for an SMS QR code is under 160 characters. Keeping the message short ensures it loads quickly, stays clear and readable when the messaging app opens, and doesn't overwhelm the user. Short messages are more likely to be sent as intended and make the action feel easy rather than like extra work.
Don't put more than 160 characters in a QR code. While almost any QR code standard can accommodate thousands, real-world success comes from real-world density. Once you've slipped the 160-char GSM-7 SMS headlock, you've put too many modules in your QR code. The density's too high and the phone's scan will fail. In our engineering delivery work, high-density QR codes cause the worst scan friction. Smaller modules require sharp focus, improved lighting, and in the field you can't control for either. Encoding no more than 160 characters together means your code remains at a version a mid-range smartphone can snap easily. If your message is too complex for such a short string, do yourself a favor and encode a short URL that does a web-based flow, not a complex SMS payload. It's easy to forget that the worst camera in your user's pocket is going to be the limiting factor, not the best.
A practical character limit for an SMS QR code is 160 characters, because SMS is built around that length and staying within it prevents the message from splitting into multiple texts. When a message breaks into two or more parts, the experience looks messy, feels slow, and lowers response rates. Keeping it under 160 keeps the user flow clean and makes the QR experience feel effortless.
When designing an SMS QR code, it's advisable to keep the message within 160 characters, aligning with standard SMS length. This promotes clarity, ensuring that users receive straightforward communications without unnecessary details. Concise messages enhance user engagement, as recipients are more likely to read and respond to short, easily digestible content.