It’s a good thing we checked! Our customer asked us to print a number of these posters for retail stores, and Ken in our shop grabbed his smart phone to be sure it would read the QR code. It didn’t! It turns our that QR codes need to be of a certain size, depending on the length of the URL they are pointing to. Who knew?
Here’s a web site that talks about the size of QR codes when they are printed.
Whats going on is that as the web address gets longer, the QR code needs to store more information. A short web address will only need a QR code with 25×25 boxes, but a long web address can get up to 57×57 or even more.
Your smart phone needs to see each dot at about .4mm to be able to read it. That means a short web addres (a 25×25) will be about 1 cm (3/8″) across on your phone. If you have a 57×57 QR code, it will need to be nearly an inch across.
For poster printing, figure the typical reading distance to be 10 times the width of the QR code. For instance, 2″ across if people will read it from a distance of 20″, which would be typical for a retail application. The code also needs to be clear enough at print size that each pixel of the code is readable. We increased the size of the QR code, and it worked fine on our customer’s poster.