What is a SKU (Stock Keeping Unit)? meaning, examples and how to create them

An SKU (stock keeping unit, pronounced "skew") is a unique code you assign to each product and variant so you can track it. It matters because once you sell more than a handful of items across sizes, colors, and locations, the SKU is how every count, order, sale, and report stays straight, and a messy scheme creates mispicks and stock errors.

This guide covers what an SKU is, how it differs from a UPC, how to build a SKU system you can live with, and a generator to create them.

What is an SKU? 

An SKU is a unique alphanumeric code, letters and numbers, that a business creates and assigns to each product and each variant. Every size, color, and style gets its own, so a red medium sweatshirt and a blue large one are different SKUs even though they are the same garment.

SKUs are internal: you design your own to match how you organize stock. They usually run about 8 to 12 characters, enough to keep every item unique while staying quick to read. A SKU exists to let you tell products apart fast, whether you are counting stock, working a pick list, or reading a sales report.

Why SKUs matter 

SKUs are what make product-level data possible because every variant carries its own code; you can see which items sell, which sit, which need reordering, and which have quietly gone missing. That last one carries real money.

The National Retail Federation's 2023 National Retail Security put retail shrink at $112.1 billion in 2022, or 1.6% of sales, up from $93.9 billion and 1.4% the year before.

Shrink is the gap between the stock your records claim and what is actually on the shelf, and you find it by counting at the SKU level.  

SKU vs. UPC vs. barcode 

SKU gets mixed up with UPCs and barcodes, so here is how the three differ:

• A SKU is your internal code, custom and alphanumeric
   

• A UPC (universal product code) is an external code, a fixed 12 digits, assigned through GS1 and identical for that product at every retailer.
   

• A barcode is the scannable image. A UPC is one kind of barcode, and your SKUs can be barcoded too.

A product keeps the same UPC everywhere it is sold, while each business that sells it assigns its own SKU.

Most businesses run both, SKUs to work in the warehouse and UPCs to sell through Amazon, Walmart, and other channels, all linked together in the inventory software.

SKU vs. model number vs. serial number 

Three more identifiers crowd the same space. What separates them is who assigns the code and what it points at:

The practical test: Two identical laptops on the same shelf share a SKU and a model number but carry different serial numbers. That is why serials drive warranties, recalls, and repairs. Building a model number into your SKU is fine, as long as the SKU still comes out unique for every variant.

What goes into a good SKU? 

A good SKU packs a few attributes into a consistent order, running from general to specific: category, then style or product, then color, then size, so every SKU reads the same way and sorts sensibly.

Encode only what stays put, since a product's category and color hold steady while its supplier and price move. Keep it short and readable, and make sure every variant is unique.

How to create an SKU system  

• List the attributes that tell your products apart: category, style, color, size, and maybe location.
   

• Fix their order, general to specific, and pick a short code for each value (RED and BLU; S, M, and L).
   

• Set the format: Decide how many characters each segment gets and which separator you use, usually a dash. Doing this before you assign anything is what keeps the scheme from drifting later.
   

• Assign the SKUs by joining the segments with a separator, usually a dash.
   

• Write the scheme down and apply it the same way every time, so anyone can read or build an SKU without guessing.

SKU examples 

A worked set for a lime T-shirt, using category-color-material-size (illustrative):

The pattern is the same each time, so a picker or a report reads it at a glance.

Readable vs. encoded SKUs 

Schemes come in two broad styles. Readable SKUs spell the attributes out, so anyone can decode them on sight. Encoded SKUs compress the same information into something shorter that needs a key:

VX-M-SHRT-T-BLU-MED Readable: Vendor X, men's, T-shirt, blue, medium

12MSTLU2 Encoded: the same product, compressed

Readable codes are easier to train staff on and to audit. Encoded codes fit small labels and give away less to customers and competitors. Pick one style and hold to it, because a catalogue that mixes both is hardest to maintain.

How real companies use SKUs 

Two familiar examples show the range.

Intel builds meaning into its processor numbers. In a Core i7-14700K, the 14 marks the generation, the digits after it mark the tier within that generation, and the K suffix marks an unlocked chip.

Amazon asks third-party sellers on FBA to supply their own seller SKU for each item and generates one when the seller does not. The scheme belongs to whoever is tracking the stock, and it only has to make sense to them.

SKU best practices and mistakes 

A few habits keep a SKU system clean, and a few errors will corrupt your data:

• Keep one consistent, documented format, running from general to specific.
   

• Stick to letters, numbers, and a simple separator (a dash or underscore). Spaces and symbols like @ or / break spreadsheet formulas and scanners.
   

• Never start a SKU with a zero. Spreadsheets and some software strip leading zeroes and corrupt the record.
   

• Keep changeable data out of the code. Price and supplier move; an SKU should stay put.

What is SKU rationalization? 

SKU rationalization is reviewing your SKUs and pruning the ones that are not earning their place. As a catalogue grows, slow, low-margin variants pile up and tie up cash and shelf space. Ranking SKUs by sales and margin every so often, then cutting or consolidating the tail, keeps the range tight. It pairs naturally with inventory turnover and dead stock, since the slow SKUs are usually the ones dragging both.

SKUs in Zoho Inventory 

Zoho Inventory gives every item a SKU and uses it across orders, counts, and reports, and you can tie each SKU to its UPC or barcode for scanning and selling across channels. Deciding on a clear SKU scheme before you load the catalogue is what keeps that tracking clean from the start.