Not too small: The standard black and white QR code itself should be around 1.5 to 2 cm or 0.59 to 0.79 inches big. Do not make individual modules smaller than 0.8 mm or 0.03 inches. Also: Be sure to leave a little bit of white space around the code (approximately 4 times the size of one module). The yellow in the example below shows the appropriate border size around the code. If you print a Design QR Code, these rules do not apply, it has to be printed bigger and needs to be tested. Ask your printer or come into our chat for help.
Can it be too big? This always depends on the distance between the person scanning the code and the code’s physical location. If you know that a customer will be standing about 65 feet/20 meters away, the code must be bigger than if he scans it from 8 inches/20 centimeters away. As a test, you may want to print your code on a piece of paper at a specific size and find out the farthest distance from which it can be scanned. A code being printed on a housewall and being scanned from the other side of the street naturally has to be much, much bigger than a code being scanned from a poster at a bus station where people scan it from a 5 steps distance.