After over 6 years publishing information about QR -Codes in this blog we have received hundreds of questions and queries through different channels.
Probably the question that would lead a TOP-10 would be: “What is the minimum size for a QR- Code?”
We usually say that this is a ” wrong question ” because there are much more important strategic issues that the size to consider before using a QR -Code . Eg.: goals, calls to action, mobilizing content, metrics, location, etc. .
An equally wrong question would be: What size should a text have?
In any case, the minimum size of a QR code is determined by a wide combination of factors and especially common sense .
Factors determining the readability of a QR -Code
1) Size / distance – it’s not just a matter of size. Combining size / distance is what determines if a QR is readable or not.
2) Number of characters. The more information a QR contains the more “dense” it will be and that will make reading it more difficult.
You could say that the more information contains the larger QR must be.
3) Level of error correction. The redundancy of information contained in a QR algorithm is given by (Red -Solomon ) pemitirá “play” with designs and customizations but that will be detrimental to readability.
4) Contrast with the base. If we use custom codes, we must control the contrast with the base (specially if you use yellow or light colors).
5 ) Phone lenses. This problem affects very smartphone cameras but if they are old they usually don’t have a good macros (ability to focus up close ) and this can also affect readibility of a QR for being too small ( < 2cm) .
6) App used . There are hundreds if not thousands of applications reading QR- Codes in the various app stores and some are better than others. They all do essentially the same: identify, capture and read 2D codes but efficiency may vary.
7) Light. Even if the contrast is correct in “lab conditions” if the QR is read in low light or in a backlighted surface (Eg. screen) it may become unreadable .
8) Angle . There is a tolerance of skewed catch the QR form 20-30 ° vertically or horizontally
9) Surface curvature. If you print a QR on a curved surface (Eg. Mug) if the size is not excessive it can be read .
We know that it is a little “scientific ” answer but the number of variables make curiously trial and error is the most reliable method to validate a QR face .
The ease, immediacy and low cost of testing makes the best way to determine the size is “try , try and try .” It is very easy to print 3-4 different sizes and see how far we can shrink the QR .
Our advice is to borrow the worst smartphone office and do the tests with this and average lighting conditions . If it works, it will always work.
Bonus for mathematical
DENSO-WAVE explanation: http://www.qrcode.com/en/howto/generate.html
We leave some links to some posts you wrote STUFF QR- mates which have a mathematical formula to calculate the size of a QR .
Minimum Size = QR Code Scanning Distance / 10
Improved formula :
QR Code Minimum Size = (Scanning Distance / Distance Factor) * Data Density Factor
As you will see at the end of their post, they also recommend the “test , test , test” methodology to determine the optimal size of a QR.