UPC and EAN Barcodes are used for both conveying pricing information to the Point of Sale Systems in stores (electronic cash registers) and maintaining inventory for the retailer.
You need as many barcodes as you have products or variations of products.
If you are selling shoes, you would need one unique barcode for each style, color and size.
If you are selling soft drinks, you would need one for the 12 oz. can, the 12 oz. bottle, the six or twelve-packs, and the liters of each flavor.
Every variation of a product needs a unique barcode.
If you only have one product and you are manufacturing one or 1,000,000 – each piece will have the same barcode number.