QR Code

- Technical Limitations

Technical Limitations Of QR Codes

If your not familiar with what a QR Code is or how it works then its worth reading What's A QR Code before continuing.
This page hopes to help understand some of the technical limitations of QR Codes and assumes you have a basic understanding of what they are.
IMPORTANT: We don't update this page any more, so for the latest and most up to date information, please visit QR Codes - What's A QR Code? or our technical series starting with QR Codes - How Much Data Can A QR Code Store?
QR Codes use a 2 dimensional matrix in order to store data. Some variables exist that impact on the amount of data a QR Code can store. The first of which is the version number (1 to 40). The main different between versions is the number of rows and columns they can hold. The highest version is version 40 which includes 177 rows and 177 columns. The more rows and columns there are, the more data it can hold.
QR Codes also allow for error correction. The level of error correction plays a part in how much data they can store. There are 4 different levels of error correction. These are L[ow], M[edium], Q[uality], H[igh]. The highest level of error correction has the ability to restore up to 30% of a corrupt code. This is achieved using Reed-Solomon Error Correction.
Based on the different error correction values above and the different versions available, The maximum storage capacity can therefor occur at 40-L. This is version 40 with error correction set to low. This QR Codes would allow for 3Kb of data to be encoded.
QR Code Capacity How this then translates into readable data is determined by the datatype in use. These have been detailed to the left. Bare in mind the 20 character limit of a traditional barcode.
The QR Code is made of up many small squares. the number of available squares is determined by the number of rows and columns a code can contains. A version 40 code would allow for a total of 31,329 squares. It's those squares in varying configurations that are able to encode data. Adjusting the surface area of the QR Code does not allow for more data to be encoded. Keep in mind however that if you make it very small then the person with the scanner will need to get very close in order to scan it, Similarly if its too large, they will need to stand way back.
Most of the time, QR Codes are black and white, black representing foreground squares and white representing background squares. You don't have to use black and white. Your scanner is only looking for 2 distinguishable sets of squares so if you want to use colour, so long as they are not too similar, you shouldn't have an issue. There's some good examples of QR Codes created with colour at QR Code - Art and you can find more details on how a scanner is able to read a colour QR Code at QR Codes - Do They Have To Be B&W?
A QR Code can also be scanned in any direction. Try it out below. These 3 QR Codes are all the same only they have been rotated 90 Degrees each time.
QR URL Example QR URL Example QR URL Example
Each QR Code has reference squares in each of its corners, 1 of the corners is always smaller than the other 3. It's these that allow the processing device to determine which way the code should be processed. For more info on the rotation of QR Codes and why it works check out QR Code FAQs - Can A QR Code Be Rotated?
QR Code Sections QR Codes are split into different sections and its these sections which help the scanner understand the code and read its content. Its these sections that allow QR Codes to be so versatile and for example be read upside down and contain error correction. For details on the different sections, see QR Code - What Are The Different Sections Of A QR Code?
Although there are many different options when creating your QR Code such as the size, versions, error correction and data type, there is an international QR Code standard in which all QR Code generators and readers should conform too. This ensures you should always be able to read and have people read your QR Codes.
If you want to go over the basics of QR Codes, then read What's A QR Code
Or take some time to read our FAQs
If you want something a little more detailed, try our technical series The Technical Stuff
Lee Taylor, 2014 - v1.4.1