Barcode classes are based on how much and what kind of data can the barcode hold

Barcodes have three main classes:

• Numeric only (linear): numbers only 0-9
• Alpha-numeric (linear): These can get tricky, code 128 allows for all ASCII characters , while code 39 only allows Uppercase letters, numbers and space -, .,$, /,+, %
• 2-Dimensional (2D): Can hold large amounts of data of various type

When choosing a barcode, it is very important to know what type of information will be coded into the barcode and what it will be used for. There are several industry standards, requiring the use of a particular barcode. The most commonly known is the UPC barcode - to identify products for resell. ISBN is another familiar barcode used only for books and media.

Example: bar coding the SKU of a product for internal purpose (such as inventory tracking.)

• First, you must know if the product SKU is numeric or alpha-numeric. If the SKU is alpha-numeric then you must find out if it has any special characters in it.
• Next, if you want the barcode to contain more that one piece of data, you may need to check into a 2d barcode.

Some linear barcodes can hold more than one piece of data, but are limited to a certain number of charters.