You cannot make up your own UPC-A barcode numbers. Every major retailer — Walmart, Target, Amazon — validates against the GS1 database. If your barcode number is not registered, it gets rejected at receiving. I saw this happen to small brands every week at Amazon.
GS1 US charges $250 for a single GTIN, $750 for a 10-product prefix. The annual renewal is $50-200 depending on revenue. Once registered, use our UPC-A generator to create your barcode image. Generate UPC-A →