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 .

## Conclusion

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 .

Simple Formula:

Minimum Size = QR Code Scanning Distance / 10Improved formula :

QR Code Minimum Size = (Scanning Distance / Distance Factor) * Data Density Factor

- http://www.qrstuff.com/blog/2011/11/23/qr-code-minimum-size
- http://www.qrstuff.com/blog/2011/01/18/what-size-should-a-qr-code-be

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.