SKU (Stock Keeping Unit)

A SKU (stock keeping unit) is a code a seller creates for each product variant to track stock and sales. One shirt design in 3 colors and 4 sizes is 12 SKUs, because each color and size combination is counted separately in the warehouse.

What is a SKU?

GS1 US, the barcode issuer in the United States, draws a clear line: a GTIN is a global identifier issued by GS1, while a SKU is a flexible internal code a business creates to track its own inventory. Several retailers can sell the same item with the same GTIN, but each one assigns it a different SKU (GS1 US, What is a GTIN, accessed October 2026).

Because you make it up yourself, a SKU does not need to be registered anywhere. What matters is one code per variant, and never reusing an old code for a different item.

How to build a SKU code

A simple pattern: [Category]-[Model]-[Color]-[Size]. For example, TS-BASIC-BLK-M is a Basic T-shirt in black, size M.

Avoid:

• Accented characters or spaces (“Black tee M”). Google Merchant Center recommends ASCII letters, numbers, underscores and dashes, 1 to 50 characters, for product IDs.
• Changing the code when the price changes. Google states that changing an ID overwrites the product and its performance history in Merchant Center and Google Ads.

SKU vs barcode vs GTIN

A barcode is the GTIN printed as bars for scanners. You can print a SKU as an internal barcode too, but it cannot replace a GTIN when a marketplace or Google asks for one.

SKUs on marketplaces and in Google Merchant Center

On Shopee, each product can have up to 2 variation groups, and each variation gets its own price and stock (Shopee Seller Centre, Listing products in the Shopee app, accessed October 2026). The attribute update tool lets sellers search by “product SKU” or “variation SKU” (Shopee Seller Centre, Attribute update tool, accessed October 2026).

Google Merchant Center recommends using the SKU as the ID [id] attribute; customers do not see it, but you use it to look up products, place bids and check performance. For products with variants, the parent SKU goes in item group ID [item_group_id] (Google Merchant Center Help, ID [id], accessed October 2026). For GTINs, Google says to submit one only if you are sure it is correct, and never to guess or make one up (Google Merchant Center Help, GTIN [gtin], accessed October 2026).

Reading ad reports by SKU

The Products tab in Google Ads shows how each Merchant Center product performs across Performance Max, Shopping, Video, App and Demand Gen. Since June 2026, Google has extended these metrics to all Performance Max networks (Google Ads Help, About Product Reporting, accessed October 2026).

Hypothetical example: a campaign spends VND 10 million and brings in VND 40 million, a ROAS of 4. Split by SKU, SKU A spends 5 million for 30 million in revenue (ROAS 6), and SKU B spends 5 million for 10 million (ROAS 2). The total hides that SKU B is dragging results down. The same logic applies when choosing which products go into GMV Max on TikTok Shop.

Frequently asked questions

Do SKU codes need to be registered?

No. A SKU is an internal code the seller sets. GTINs are issued by GS1.

What is the difference between a product SKU and a variation SKU?

The product SKU covers the whole design; the variation SKU identifies one variant, such as a color and size. Stock and reports should run on variation SKUs.

If you need to read marketplace ad performance product by product, see Adtek’s Brand Commerce page.