how do barcodes work

How Do Barcodes Work?

Now that you know the fascinating history of the barcode, 2 easy ways you can obtain barcodes, and the different kinds of barcodes out there, let’s get back to the basics: how do barcodes work?

To get some answers, I checked out this great video from In One Lesson, and here’s what I found out!

To begin with, let’s look at a sample barcode:

how do barcodes work


Barcode Columns

Barcodes are scanned—and as a result, read—by a laser.  Lasers read them like many countries read books: from left to right.

In the brief time this occurs, the laser will scan through the 95 evenly-spaced barcode columns and see if the columns reflect either 1) a lot of laser light or 2) absolutely none.

Each laser is connected to a computer, and computers can only recognize two numbers: 1s and 0s. Any columns that reflect a lot of light are read as a 0.  Meanwhile, the columns that reflect no light whatsoever are read as 1.

As the barcode is read, the computer will come up with a resulting number that is 95 digits long that corresponds to each column. (The number itself, of course, will only consists of 1s and 0s.)

These 95 digits are split up into 15 different sections:

  • 12 sections that are utilized for the numbers you see at the bottom of the barcode
  • 3 sections that are used as guards where barcodes begin and end: guards on the far left, center guards, and guards on the far right

All codes on the left side have an odd number of 1s, and the codes on the right side have an even number of 1s.

The reason that the codes on the left and the codes on the right have different numbers is so that the computer can identify if the barcode is being read right-side up (from left to right) or upside down.

If the computer identifies that the barcode is being read upside down, it can immediately just flip it around so it’s scanned correctly.

In addition to these guards, the barcode contains other error checks. For instance, the digits on the left always begin with a 0 and end with a 1. The right-side digits are the exact opposite, beginning with a 1 and ending with a 0.


Bottom Barcode Numbers

Now, let’s look at the bottom numbers of the barcode—the numbers we can actually see with our naked eyes.

See that 0 on the far-left side?


how barcodes work 1


That tells us what kind of barcode it is.  0 is your standard barcode.  Other options might be 2 for weighed items, 3 for pharmacy, 5 for coupons, etc.

The next set of numbers you see—12345—represents who the product manufacturer is.


how barcodes work 2


Lastly, the second set of numbers—67890—presents the product’s specific code.


how barcodes work 3

So now we come to that last number on the far-right side: the 5.


how barcodes work 4

This is a bit more complicated than the other numbers in this barcode and is called the modulo check character. 

To get the modulo check character, we need to follow a particular formula.

To start with, you’ll need to assign positions to each number at the bottom of this barcode except the last one.

1=0, 2=1, 3=2, 4=5, 6=5, and so on.

Next, you need to group all of the odd number positions together and all of the even number positions together.

So: position 1+position 3=0+2. This becomes:


(0+2+4+6+8+0) + (1+3+5+7+9)


Add them up, and you get:


(20) + (25)


Then you need to multiply the first sum (the odd number position sum) by 3:


3(20) + 25


Which leads to:


60 + 25 = 85


Now, you need to figure out the next highest multiple of 10 after 85. In this case, it’s 90.

Afterwards, subtract the total from 90.

90 – 85 = 5


Voila! We get 5—our modulo check character.


So the next time you print a barcode on a label or even scan a barcode yourself at the supermarket, keep in mind how surprisingly complicated a barcode is—and the intricate and complicated thought that went behind it. This is the same kind of thought that TSC takes to developing our printers, tools, and other technologies.

Do you have any questions about barcodes, how they’re made, or barcode printers? Let us know!





2 responses to “How Do Barcodes Work?”

  1. I had no idea that there were 95 lines on a barcode. My uncle would like to open a store and needs to put barcodes on his products. It may be a good idea for him to find a way to scan his barcodes.

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