What is the formula to calculate a QR Code's maximum data?

1
votes

I've Google'd and read quite a bit on QR codes and the maximum data that can be used based on the various settings, all of it being in tabular format. I can't seem to find anything giving a formula or a proper explanation of how these values are calculated.

What I would like to do is this:

  • Present the user with a form, allowing them to choose Format, EC & Version.
  • Then they can type in some data and generate a QR code.

Done deal. That part is easy.

The addition I would like to include is a "remaining character count" so that they (the user) can see how much more data they can type in, as well as what effect the properties have on the storage capacity of the QR code.

Does anyone know where I can find the formula(s)? Or do I need to purchase ISO 18004:2006?

3
c#qr-code
possible duplicate of Formula to calculate the max data capacity for QR codes? – Peter O.
kind of, but surely someone has used a formula to fill in the table mentioned. I'm after the formula, seems like a lot nicer way to do things than have a large, hard-coded array. – Trent
Nevertheless, a table is the easiest way to go. Unless, of course, your app is intended to run on a memory-constrained environment, which doesn't appear to be the case here. – Peter O.

3 Answers

0
votes

A formula to calculate the amount of data you could put in a QRcode would be quite complex to make, not mentioning it would need some approximations for the calculation to be possible. The formula would have to calculate the amount of modules dedicated to the data in your QRCode based on its version, and then calculate how many codewords (which are sets of 8 modules) will be used for the error correction.

To calculate the amount of modules that will be used for the data, you need to know how many modules will be used for the function patterns. While this is not a problem for the three finder patterns, the timing or the version/format information, there will be a problem with the alignment patterns as their number is dependent on the QRCode's version, meaning you anyway would have to use a table at that point.

For the second part, I have to say I don't know how to calculate the number of error correcting codewords based on the correction capacity. For some reason, there are more error correcting codewords used that there should to match the error correction capacity, as for example a 6-H QRCode can correct up to 32.6% of the data, instead of the 30% set by the H correction level.

In any case, as you can see a formula would be quite complex to implement. Using a table like already suggested is probably the best thing you could do.

0
votes

I wrote the original AIM specification for QR Code back in the '90s for Denso Corporation, and was also project editor for both editions of the ISO/IEC 18004 standard. It was felt to be much easier for people producing code printing software to use a look-up table rather than calculate capacities from a formula - no easy job as there are several independent variables that have to be taken into account iteratively when parsing the text to be encoded to minimise its length in bits, in order to achieve the smallest symbol. The most crucial factor is the mix of characters in the data, the sequence and lengths of sub-strings of numeric, alphanumeric, Kanji data, with the overhead needed to signal each change of character set, then the required level of error correction. I did produce a guidance section for this which is contained in the ISO standard.

-1
votes

The storage is calculated by the QR mode and the version/type that you are using. More specifically the calculation is based on how 'compressible' the characters are and what algorithm that the qr generator is allowed to use on the content present.

More information can be found http://en.wikipedia.org/wiki/QR_code#Storage