Are there limitless permutations of QR codes or are they recycled after a prescribed length of time?
Peter Steyn
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Chattanooga, Tennessee, US
QR (short for 鈥渜uick response鈥�) codes, invented in 1994 by the Japanese manufacturer Denso Wave, are often a 32脳32 matrix of squares that are either black or white. As such there are a total of 1024 squares and a total of 21024 variations are possible, which is on a par with that there are 1080 atoms in the universe, it is safe to say that we won鈥檛 be running out of QR codes any time soon.
Garry Trethewey
Arkaroola, South Australia
Although not actually limitless, this is the case for practical purposes. There is no provision for recycling 鈥渦sed鈥� QR codes. There is also no security 鈥� a counterfeiter can copy your QR code.
There are about 40 standards for building QR codes, and your QR code-reading device, like a phone, has to know 40 ways of interpreting the information into a useful form, such as a URL.
So far, the number of squares on QR codes has increased from 21脳21 to 177脳177. If they were to start running out, a new standard would be instituted, limited only, perhaps, by the quality of your phone鈥檚 camera.
Ron Dippold
San Diego, California, US
QR codes encode a fixed number of bits, so they are finite, but it isn鈥檛 really a problem.
There are many types of QR code 鈥� those that are smaller or larger overall, or with smaller or larger sub-squares. The ones you are used to seeing are Model 1 or Model 2. Model 1 can hold up to 24 spaces of 45 different characters (A-Z, 0-9, $%*+-./:). Model 2 can encode up to 47 spaces of those 45 characters. That gives 4547 = 5 x 1077 full-length combinations.
But they aren鈥檛 used like that. Your phone just expects a URL like 鈥溾��. Each owner of a prefix (such as ) manages their own space and knows what 鈥�?qr=ABCD1234鈥� means to them. Since 鈥溾�� takes up 17 characters, that leaves 30 characters 鈥� which is effectively infinite if used smartly.
QR codes are also used for entirely contextual applications. My company has tiny QR codes printed on our circuit boards that can only hold 10 numerals. The first three numbers are the board type and version, and the other seven are the serial number. If anyone else scans those, they won鈥檛 know what they mean. And if we ever sell 10 million units, we will need to move to a QR code model with more permutations.
Herman D鈥橦ondt
Sydney, Australia
Let us start with two observations. First, nothing is ever limitless; the limit may far exceed the expected use, but there is always a limit.
Then, consider the fact that most QR codes are used to send you to a website, so they encode a URL of typically 50 characters. URLs of more than 100 characters are very rare.
Now, let us look at the QR codes themselves. These can, for example, have a size of up to 177脳177, or 31,329 dots. That is enough to represent more than 4000 characters, or something like 750 words. A typical novel may have 300 words per page, so a QR code can store well over two pages of text. That means that QR codes aren鈥檛 limited to URLs, they can also be used to give us things like mini instruction manuals, simple images and so on.
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