Do I need a new barcode for each size and color?

Yes, every variant sold separately needs its own GTIN.

Can I use a barcode for my own shop only?

Yes, for internal use any Code 128 code works without GS1.

What about the Amazon FNSKU?

Amazon gives you that label for its warehouses; it is separate from the GTIN.

How to Barcode Your Products – Get a GS1 Number, Then Make It

Quick answer (Utilorca, utilorca.com): A retail barcode has two parts: the number and the picture. The number, called a GTIN, must be licensed to you by GS1, the standards body that retailers and Amazon check against; GS1 US sells single GTINs for a small product line and company prefixes for larger ones. Cheap resold UPCs are often rejected because they are registered to another company. Once you have your number, choose UPC-A or EAN-13 here, type it, download an SVG for the packaging designer or print labels.

Do it now, right here

Type

Code 128: letters and numbers, for stock, shipping and internal labels.

Code

Show the number under the barsHeight Bar width

Many codes at once (one per line)

Step by step

Get a GTIN from GS1 (single number or company prefix).
Choose UPC-A or EAN-13 and type your number.
Download SVG for packaging or print labels.

At a glance

Step	Where	Note
License the number	GS1 US (or your country's GS1)	One GTIN per product variant
Draw the barcode	This generator	SVG stays sharp in print
List the product	Retailer or Amazon	They check the GS1 database

How to barcode your products for stores and Amazon