What Is a SKU? Stock Keeping Units Explained

What Does SKU Stand For?

SKU stands for Stock Keeping Unit. The term comes from retail and warehouse management, where every distinct item that can be stocked, sold, or shipped needs a unique identifier so the system can tell it apart from everything else on the shelf.

The key word is unique. A blue T-shirt in size M and the same T-shirt in size L are two different SKUs — they occupy separate bin locations, have different stock levels, and fulfill different customer orders. If you treat them as the same product, your inventory count will be wrong the moment anyone buys one.

SKUs are defined by you, for your own business. There is no industry-standard format, no registration body, and no fee. You decide what the SKU looks like and what it means. Most SKUs are a short string of letters and numbers, such as SHIRT-BLU-M or TF-042-RED, stored inside your ERP, Shopify store, or spreadsheet. They never need to appear on a public database or external system.

SKU vs Barcode vs UPC — What’s the Difference?

These three terms get mixed up constantly. Here is a clear breakdown:

The simplest way to think about the difference: a SKU is "what your business calls this product." A UPC or EAN is "what the entire global retail system calls this product." A barcode is simply the visual format — the pattern of bars and spaces — that lets a scanner read either of those numbers without a human typing it in.

You can encode your own SKU into a Code 128 barcode for internal warehouse scanning without ever registering anything with GS1. That is exactly what most small and mid-size businesses do.

How to Create a Good SKU System

A well-designed SKU system saves time on every receiving, picking, and inventory count task. Here are the principles that make SKUs genuinely useful:

• Make it human-readable. JACKET-BLK-XL is far easier to double-check by eye than 00142. When a picker grabs the wrong item, a readable SKU lets them catch the error without scanning.
• Use a consistent hierarchy. Decide on a structure — category, color, size, or brand, model, variant — and apply it uniformly across every product line. Mixing formats creates confusion in reports and spreadsheets.
• Keep it between 5 and 15 characters. Shorter SKUs are faster to type and produce narrower barcodes, which are easier to print on small labels. Very long SKUs create wide Code 128 barcodes that may not fit on a 1×1.5 inch label.
• Avoid ambiguous characters. The letter O and the digit 0, or the letter I and the digit 1, look identical in many fonts. Drop them from your SKU alphabet, or use a barcode font for labels so the scanner handles the ambiguity instead of a human eye.

Some format patterns by industry:

Can a SKU Be a Barcode?

A SKU on its own is just a text string — JACKET-BLK-XL printed on a label is human-readable but cannot be scanned by a barcode gun. To make it scannable, you encode it into a barcode symbology.

Code 128 is the standard choice for SKU barcodes. It can encode the full ASCII character set — uppercase letters, lowercase letters, digits, and common punctuation — so it handles any SKU format you are likely to use. Code 128 is what you will see on most warehouse bin labels, internal product stickers, and pick lists.

The resulting label typically shows the Code 128 barcode symbol on top, with the human-readable SKU text printed below it. A warehouse worker can scan it with a gun or verify it by eye. No GS1 registration is required. No external system needs to recognize it — only your own scanners and software do.

This is entirely different from a UPC-A or EAN-13 barcode, which encodes a globally registered number. If you only need internal tracking, Code 128 + your own SKU is all you need.

When Should You Use SKU vs UPC / EAN?

The answer depends on where your products are sold and who needs to scan them:

• Online store, wholesale, or direct-to-customer only: SKU encoded as Code 128 is sufficient. You control the scanners, you control the lookup table. No registration needed.
• Retail shelf placement (supermarkets, Target, Walmart, Costco): You must have a GS1-registered UPC-A (United States) or EAN-13 (international). Retailers' POS systems look up products in global databases by these numbers.
• Amazon product listings: Amazon requires a UPC, EAN, or ISBN for most categories, though GTIN exemptions are available for private-label brands. Check Amazon's current requirements for your category.
• Internal warehouse operations: Always use SKU + Code 128, even if you also have a UPC. Your warehouse runs faster with your own codes — you do not want to look up a 12-digit UPC in a pick list when a short SKU like HONEY-500G-B12 tells you everything you need.

How to Turn Your SKU List into Barcode Labels

Once you have a clean SKU list, generating printable barcode labels takes minutes. The workflow is straightforward: