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Minimum Practical Size of a QR Code

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Problem:

We have used QR Codes on multiple occasions for a variety of purposes: to ease the download of our native mobile apps, to ease access to our mobile web apps, to use as short cuts to content within our apps, for scavenger hunts, etc.  In most cases we encourage events and venues to print large QR codes on posters to attract attention and be scan to read from a distance. It was important to keep in mind that the more data embedded in a QR code, the higher density the module must be, making the scanning increasingly difficult. In the end it all comes down to whether the camera can actually see the smallest bit in the QR image, or the individual modules. It is necessary to keep in mind that the smaller the QR code, the smaller each individual element, and the closer the camera will need to be to ensure a proper scan.
We are now in the process of implementing an app for a venue at which the QR Codes need to be subtler and as small as possible.  We weren’t sure what size was “as small as possible” yet would still be reliably readable by an iPhone or Android phone.  Some quick Google searches did not turn up a simple answer, so we did a quick (semi-scientific) experiment.

Process:

We printed QR codes at 2 different densities in 12 different sizes for a total of 24 images.  The 12 sizes ranged from 2.5″ to .25″ wide.   The lower density was a 29×29 matrix of QR code “modules”; the higher density was 33×33. For the purpose of standardization, the QR codes used were black pixels, on a white background.

The phones we tested were the iPhone 4s, iPhone 4, Android LG Optimus V, and the Android Galaxy.  For QRC scanning we used the ZBar app on the iPhone and QR Droid on Android.

We tested all 4 phones, 12 QRC sizes, 2 QRC densities, in low and bright office (fluorescent) lighting.  In each test we recorded the maximum range (distance between paper and phone) at which the phone successfully scanned the QR code.

Results:

In the table below the color indicates the reliability of scanning – green meaning very reliable, red meaning failure.

  • According to our results, the smallest practical size for a printed QR code is between 1.25” and 1.75″.
  • The density of the QR code mattered less than we anticipated.
  • Low lighting did not significantly reduce the maximum range.
  • The Android phones had more trouble focusing in low light situations but had much better range than the iPhones.

 

QR
Code
Read
Distance
Size Device Low Density High Density Low Light:
Max Range Max Range
2.5″ iPhone 4s 18″ 18″ In low light, no problem
iPhone 4 18″ 18″ In low light, no problem
Android LG Optimus V 36″ 36″ Takes a while to focus in low light
Android Galaxy 36″ 36″ Takes a while to focus in low light
2″ iPhone 4s 16″ 16″ In low light, no problem
iPhone 4 16″ 16″ In low light, no problem
Android LG Optimus V 30″ 30″ Takes a while to focus in low light
Android Galaxy 30″ 30″ Takes a while to focus in low light
1.75″ iPhone 4s 17″ 17″ In low light, no problem
iPhone 4 16″ 16″ In low light, no problem
Android LG Optimus V 30″ 30″ Takes a while to focus in low light
Android Galaxy 30″ 30″ Takes a while to focus in low light
1.5″ iPhone 4s 13″ 13″ In low light, no problem
iPhone 4 12″ 12″ In low light, no problem
Android LG Optimus V 24″ 24″ Takes a while to focus in low light
Android Galaxy 24″ 24″ Takes a while to focus in low light
1.25″ iPhone 4s 10″ 8″ Takes a while to focus in low light
iPhone 4 10″ 8″ Takes a while to focus in low light
Android LG Optimus V 18″ 18″ Takes a while to focus in low light
Android Galaxy 18″ 18″ Takes a while to focus in low light
1″ iPhone 4s 6″ 6″ Takes a while to focus in low light
iPhone 4 6″ 6″ Takes a while to focus in low light
Android LG Optimus V 12″ 12″ Takes a while to focus in low light
Android Galaxy 12″ 12″ Takes a while to focus in low light
.75″ iPhone 4s 6″ 6″ Takes a while to focus in low light
iPhone 4 6″ 6″ Takes a while to focus in low light
Android LG Optimus V 8″ 8″ Will not read in low light
Android Galaxy 8″ 8″ Will not read in low light
.66″ iPhone 4s Takes a while to focus in low light
iPhone 4 5″ 4″ Takes a while to focus in low light
Android LG Optimus V 6″ 6″ Will not read in low light
Android Galaxy 6″ 6″ Will not read in low light
.5″ iPhone 4s 4″ 4″ Takes a while to focus in low light
iPhone 4 4″ 3″ Takes a while to focus in low light
Android LG Optimus V 6″ 6″ Will not read in low light
Android Galaxy 6″ 6″ Will not read in low light
.4″ iPhone 4s 4″ 4″ Takes a while to focus in low light
iPhone 4 4″ 4″ Will not read in low light
Android LG Optimus V 6″ 5″ Will not read in low light
Android Galaxy 6″ 5″ Will not read in low light
.33″ iPhone 4s NO READ NO READ NO READ IN ANY CONDITIONS
iPhone 4 NO READ NO READ NO READ IN ANY CONDITIONS
Android LG Optimus V 5″ 4″ Will not read in low light
Android Galaxy 5″ 4″ Will not read in low light
.25″ iPhone 4s NO READ NO READ NO READ IN ANY CONDITIONS
iPhone 4 NO READ NO READ NO READ IN ANY CONDITIONS
Android LG Optimus V NO READ NO READ NO READ IN ANY CONDITIONS
Android Galaxy NO READ NO READ NO READ IN ANY CONDITIONS


Next Steps:

Our test was obviously not exhaustive and could have been far more scientific. If anyone would like to continue the experiment, we’d recommend the following improvements:

  • Test in both natural and artificial lighting
  • Use a wider range of Android devices
  • Experiment with different QR scanning software – for example, QR Droid only lets part of what the camera views be scanned, meaning it needs to be further away from the code than other programs may need.
  • Measure the distance between the camera and the QR code more precisely
  • Define “low light” and “bright light” environments more scientifically
  • Use a wider range of QRC densities
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