Home   Contact   About     |   PCL Barcode Fonts   |   Information about Barcodes  

A Short Introduction to Barcodes

Here is some information that will give you a basic introduction to barcodes. If you need more details about particular barcodes, check out our page on different types of barcodes. And we are always happy to answer questions; just email us at

How does a barcode work?

how_it_works Each character is represented by a pattern of wide and narrow bars. A barcode scanner uses a photosensor to convert the barcode into electrical signals as it moves across a barcode. The scanner then measures the relative widths of the bars and spaces, translates the different patterns back into regular characters, and sends them on to a computer or portable terminal.

Every barcode begins with a special start character and ends with a special stop character. These codes help the reader detect the barcode and figure out whether it is being scanned forward or backward.

how_it_works2 Some barcodes may include a checksum character just before the stop character. A checksum is calculated when the barcode is printed using the characters in the barcode. The reader performs the same calculation and compares its answer to the checksum it read at the end of the barcode. If the two don't match, the reader assumes that something is wrong, throws out the data, and tries again.

There are different barcode symbologies, each with its own particular pattern of bars. The UPC code used on retail products is an all-numeric code; so is the Interleaved 2 of 5 Code. Code 39 includes upper case letters, digits, and a few symbols. Code 128 includes every printable and unprintable ASCII character code.

What's a 2D code?

Data Matrix 2-Dimensional symbols are generally square or rectangular patterns that encode data in two dimensions. They fall into two general categories: 'Stacked barcodes' are constructed like a layer cake of barcodes stacked one on top of the other; they can be read by special 2-D scanners or by many CCD and laser scanners with the aid of special decoding software. 'Matrix Codes' are built on a true 2-D matrix; they are usually more compact than a stacked barcode, and they can be read only by a true 2-D scanner (imager). The primary advantage of 2-D codes is the ability to encode a lot of information in a small space.

Widely-used 2D codes include DataMatrix (pictured above), PDF-417, and the QR Code.

How much data can a barcode hold?

The practical limit for a standard linear barcode depends on a number of factors, but 20 to 25 characters is an approximate maximum. All-numeric data takes less space than mixed alpha-nuumeric data. 2D symbols can encode up to as many as 2,000 characters.