A SKU, short for stock keeping unit, is the unique alphanumeric code a retailer assigns internally to track one specific sellable item — down to the exact size, color, or configuration — across inventory systems, point of sale, and product feeds. Unlike a GTIN or UPC, which is issued externally and shared industry-wide, a SKU is defined entirely by the business using it, which means the same physical product can carry a different SKU at every retailer that sells it. Because it's built for internal tracking rather than public identification, a SKU is often the field a feed relies on most heavily to keep inventory and listings in sync.

Why SKU Matters for Feed Accuracy

A SKU is frequently the thread connecting a feed row back to the exact inventory record it should be tracking, which makes it central to keeping stock levels, pricing, and availability accurate across every channel a product is listed on. When a SKU is inconsistent between a retailer's inventory system and its feed — duplicated, reused after a product is discontinued, or simply mistyped — availability and pricing quietly fall out of sync, and a channel keeps selling a product that's actually gone. This is one of the more common sources of feed errors serious enough to trigger account-level suspensions, since platforms treat mismatched identifiers as a signal the underlying catalog data can't be trusted.

How SKU Works

Each variant of a product typically gets its own SKU, since a SKU is meant to identify one specific, individually trackable unit rather than a product family. In a feed, the SKU often populates the id field directly or is carried alongside it as a reference value, letting inventory management systems and the feed stay mapped to the same underlying record. Because SKUs are internal, they can follow whatever convention a retailer prefers — some encode category, color, or size directly into the code, while others are simply sequential — as long as the value stays stable and unique for the life of that specific item.

Example: SKU as the Feed Identifier

<item>
  <g:id>APP-JCKT-BLK-L</g:id>
  <title>Technical Shell Jacket - Black, L</title>
  <g:item_group_id>TECH-SHELL-2024</g:item_group_id>
  <g:mpn>APP-JCKT-BLK-L</g:mpn>
  <g:gtin>00887654321098</g:gtin>
  <g:availability>in stock</g:availability>
  <g:price>210.00 USD</g:price>
</item>

Here the SKU (APP-JCKT-BLK-L) doubles as both the feed's g:id and its g:mpn, while the g:gtin remains a separate, externally issued code — a common pattern that lets a retailer's own inventory system and a shopping platform's product-matching logic both work from identifiers that mean something to each of them.

Related Concepts

A SKU only does its job properly when it's unique down to the variant level and stays aligned with whatever item group ID clusters that variant with its siblings, since both fields depend on each other to keep a feed's structure coherent. Getting SKU and identifier hygiene right across a catalog is also foundational to inventory management, and retailers cleaning up mismatched identifiers can find a practical walkthrough in Fix Common GTIN and Product Identifier Errors in Your Shopping Feed.