In inventory management, a stock keeping unit, abbreviated SKU, is the unit of measure in which the stocks of a material are managed. It is a distinct type of item for sale, purchase, or tracking in inventory, such as a product or service, and all attributes associated with the item type that distinguish it from other item types, which for a product can include manufacturer, description, material, size, color, packaging, and warranty terms (Wikipedia, Stock keeping unit).
The second half of that definition is the working part. A SKU is not the product as a shopper thinks of it. It is the product plus every attribute that has to be told apart from another, so one shirt design in four sizes and three colours is twelve stock keeping units, not one.
The Unit and the Code Are Two Different Things
The term does double duty, and confusing the two is the source of most disagreements about how many SKUs a business has.
The unit. When a business records the inventory of its stock, it counts the quantity it has of each unit, or SKU (Wikipedia, Stock keeping unit). Used this way the word names a bucket that a count goes into.
The code. SKU can also refer to a unique identifier or code, sometimes represented via a barcode for scanning and tracking, which refers to the particular stock keeping unit (Wikipedia, Stock keeping unit). Used this way the word names the label on the bucket.
SKUs Are Not Standardized, and That Is the Whole Point
These identifiers are not regulated or standardized, and when a company receives items from a vendor it has a choice of maintaining the vendor’s SKU or creating its own (Wikipedia, Stock keeping unit). Two businesses selling the identical item will normally carry different SKUs for it, and neither is wrong.
That is what separates a SKU from an identifier issued under a standard. A Global Trade Item Number can be used by a company to uniquely identify all of its trade items, and the standards body defines trade items as products or services that are priced, ordered or invoiced at any point in the supply chain (GS1, Global Trade Item Number (GTIN)). The Universal Product Code, the European Article Number and the Australian Product Number are special cases of GTINs (Wikipedia, Stock keeping unit).
So the practical rule is that a GTIN travels between companies and a SKU does not. A barcode scanned at two different retailers will resolve to the same GTIN and to two different SKUs.
Where SKUs Meet the Accounting Records
A business does not get to decide whether inventory is counted. In most cases, a business in which the production, purchase, or sale of merchandise was an income-producing factor must take inventories into account at the beginning and end of the tax year (IRS, Instructions for Schedule C (Form 1040), 2025). The SKU is the level that count happens at, which is why the granularity chosen for the operational system decides what the accounting system can later prove.
That constraint is sharpest on cost flow. A system that reports an average by SKU cannot support a method that requires unit-level cost, whatever the written policy says, and that boundary is worked through in specific identification method. The alternatives, and how each one moves cost out of inventory, sit in inventory retail method and cost of goods available for sale formula.
The small business taxpayer exception is the one place the requirement softens. A qualifying business can choose not to keep an inventory, but it must still use a method of accounting for inventory that clearly reflects income (IRS, Instructions for Schedule C (Form 1040), 2025), and the two conditions that qualify a taxpayer for it are set out in Schedule C.
What a SKU Is Confused With
A Barcode
A barcode is a way of representing an identifier so a scanner can read it, not the identifier itself. A SKU is sometimes represented via a barcode (Wikipedia, Stock keeping unit), and so is a GTIN, which is why the same printed symbol can be described as either depending on which number it encodes.
A Product
One product can be many SKUs, because every distinguishing attribute creates another one. That is why a catalogue count and a SKU count answer different questions, and why the ratio between them tells you how much variation the business is carrying.
A Serial Number
A SKU names a type. A serial number names one physical item of that type. Counting stock uses the first; tracing a single unit through a warranty claim uses the second.
Common Questions
To make the count possible at the level decisions are made at. Because a SKU carries all the attributes that distinguish one item type from another (Wikipedia, Stock keeping unit), counting by SKU is what lets a business see that one size is moving and another is not, which a count by product cannot show. How fast those counts turn over is measured in inventory turnover.
Only through what it makes provable. Nothing in the tax rules prescribes a SKU scheme. What the rules require is that inventories be taken into account and that the method used clearly reflect income (IRS, Instructions for Schedule C (Form 1040), 2025), and a system whose units are coarser than its costing method assumes cannot meet the second of those.
Accountably places trained offshore accountants inside US CPA and EA firms, and a firm can run a real block of its own inventory and close work through a trial task before anything client facing depends on it.
