When not to use a QR code

The four disqualifying conditions

1. The audience is moving. A driver at 50 km/h covers 14 m per second. There is no sequence of events in which a passenger unlocks a phone, opens the camera and frames a billboard code. The same applies to escalators, station concourses at rush hour, and anything on a vehicle in motion.

2. The user is already on a device. A QR code on a web page, in an email, or in a PDF read on a laptop asks someone to pick up a second device to do what a link would do in one tap. Show a link; show a code only when a second device is genuinely likely.

3. It would be the only route. Allergen information, safety instructions, statutory notices, benefit applications, aftercare guidance. Anyone without a smartphone, without data, with low vision, or with a flat battery is excluded. In several jurisdictions that is a legal exposure, not just poor service.

4. There is not enough physical room. Printed width must be at least the viewing distance divided by ten. If a shelf-edge strip gives you 1 cm and the payload needs 2 cm, the answer is a shorter payload or no code — not a smaller code.

The cases people get wrong most often

• Business cards where the code is 1 cm and encodes a full vCard. The modules end up below what a press can print.
• Billboards. See above.
• Codes on a website "so people can share it to their phone" — a share sheet does this better.
• Codes with no reason attached. A bare code in the corner of a poster gets ignored.
• Codes pointing at a homepage. The scanner has to search for what you meant.
• Foil, embossed and dark-on-dark codes that look beautiful and do not scan.

The test

Before printing, answer these:

1. Will the reader be standing still for at least ten seconds?
2. Is there a stated reason to scan, in words, next to the code?
3. Is the code at least viewing distance ÷ 10 wide?
4. Does the destination work on a phone, on cellular, in one second?
5. Is there a non-QR alternative for people who cannot use it?

Two or more "no" answers means the code is decoration.

FAQ

Do QR codes work on billboards?

Effectively no. The ten-to-one rule means a 30 m viewing distance needs a 3 m code, and drivers cannot scan while moving. Use out-of-home codes only where the audience is stationary, such as bus shelters and lift lobbies.

Should I put a QR code on my website?

Only if a second device is genuinely likely — for example, a code to open a page on a phone from a desktop. Otherwise a link does the same job in one tap.

Can a QR code replace printed safety information?

No. Anyone without a smartphone, data, or usable vision is excluded, and in many jurisdictions that is a legal problem as well as a practical one.

What size is too small?

Anything below the viewing distance divided by ten. If the available space is smaller than that, shorten the payload so the code has fewer modules — do not just shrink the code.