How Big Does a QR Code Need to be for Printing?
QR Codes (Quick Response Codes) are very useful tools that can be used to add interaction with a static printed piece. They can be used to link to a URL, compose an E-Mail or text message or imbed contact information in the form of a VCard. All of these capabilities are great, but you have to print the code at a size that can actualy be read by the end user. This page hopefully will give you a better understanding of how to determine the best size to print a QR Code.
(Number of Modules) X (0.03 in)
Parts of a QR Code
A QR Code is made up of small squares on a high contrast background. Black squares on a white background give the best results. Each square is called a module. The key to sizing a QR Code is making sure that each module is large enough that it can be seen by the QR Code reader. There are certain modules that will always be on a QR Code. There are three "position" squares in the corners that are 8x8 modules in size, as well as one or more "alignment" square that is 5x5 modules. These square are used to align the image if you are scanning it at an angle. There are also "timing" modules that run on two sides of the QR Code connecting the "position" squares. Since a QR code is always a square these alternating black and white "timing" modules alow the reader to measure the total size of a QR code. and double check that it can see the whole thing since the number of "timing" squares should be the same in both directions. There is also other required information that tells the QR Code reader what version and format the code is using so that the reader knows how to interpret the code.
Types of QR Codes
There are forty different versions of QR Codes. The version is directly tied to the number of modules, which ranges from 21x21 with version one to 177x177 modules with version forty. As you add modules and increase the size the amount of data you can store increases. This is not a direct linear increase because, within each version there are four levels of error correction. The amount of error correction determines how many of the modules in the data portion of the QR Code are used to double check and confirm that the stored information is correct. If you have a QR Code with a high level of error correction it will be easier to read if it gets damaged or is not printed with high contrast colors. The error correction (ECC) will also limit the amount of information that can be stored since some of the modules are being used for backup.
For example a version 1 QR Code that is 21x21 modules with the minimum level of error correction (~7%) can store 25 alpha numeric characters. A version 2 QR Code that is 25x25 characters with the highest level of error correction (~30%) can only store 20 alpha numeric characters.
Limitations of QR Code Readers
There is one more big variable in the equation when it comes to what size your QR Code needs to be when printing. That limitation is with the actual reader. Most QR Codes are read with a camera on a phone. The quality of the cameras on these phones varies greatly, so unfortunately you have to size a QR Code for the lowest common denominator. What this basicly means is that for a 1MP (Megapixel) camera on a phone the modules on a QR Code will need to be much larger for the phone to be able to distinguish one from another. On a much newer and better phone it might have an 8MP Camera which would mean that each module can be much smaller and still be read. As technology progresses the size that the codes have to be printed will continue to shrink. For the time being it is suggested that you make each module at least 0.03". To determine the minimum sixe of a QR code count the modules and multiply that number by .03 inches).
(Modules) X (0.03 in)