A SKU (stock keeping unit) is a code a seller creates to identify one specific product in their own inventory. Each variation gets its own SKU, so a blue T-shirt in medium and the same shirt in large are two SKUs. SKU is pronounced “skew”. Unlike a UPC barcode, a SKU is internal: you choose the format, and the same product can have a different SKU at every company that sells it.
This guide explains what a SKU number means, how it differs from a UPC, ASIN and other product codes, how to create SKUs that scale, and how to use them when you sell on several marketplaces.
What does SKU stand for?
SKU stands for stock keeping unit. In practice people use the word in two ways:
- The code itself, for example TSH-BLU-M. This is the SKU number, even though it usually contains letters too.
- A distinct item you stock. “We carry 400 SKUs” means 400 different sellable items, counting every size and color separately.
What is a SKU used for?
- Tracking inventory: how many units of each exact item you have, and where.
- Picking and packing: warehouse staff pick by SKU, not by product title.
- Reordering: reorder points and sales forecasts are set per SKU.
- Reporting: sales, returns and profit per SKU show which variations earn money.
- Connecting sales channels: one SKU ties the same item together across your store and every marketplace.
SKU vs UPC vs ASIN vs other codes
| Code | Who creates it | Same for every seller? | Where it is used |
|---|---|---|---|
| SKU | You, the seller | No | Your inventory, orders and reports |
| UPC / EAN (GTIN) | GS1, through the brand owner | Yes | Retail barcodes and marketplace catalogs worldwide |
| ASIN | Amazon | Yes, on Amazon | Amazon product pages only |
| FNSKU | Amazon | No, it is tied to your account | Labels on units stored in FBA |
| MPN | The manufacturer | Yes | Manufacturer part catalogs |
The short version: the UPC says what the product is everywhere, the SKU is your own name for it. See what an ASIN is and our FNSKU labeling guide for the Amazon codes.
SKU number example
A good SKU is short and readable, and moves from general to specific:
| Part | Meaning | Example |
|---|---|---|
| Product type | T-shirt | TSH |
| Style or model | Classic crew neck | CRW |
| Color | Blue | BLU |
| Size | Medium | M |
| Full SKU | TSH-CRW-BLU-M |
How to create SKU numbers
- Decide the attributes that matter: usually product type, model, color and size, in that order.
- Use short codes of two to four characters for each attribute and keep a list of them.
- Keep the whole SKU short, ideally 8 to 16 characters, so people can read and type it.
- Use only letters, numbers and dashes. Avoid spaces, slashes and symbols that break spreadsheets and marketplace uploads.
- Avoid characters that look alike, such as the letter O and zero, or the letter I and one.
- Don’t start with zero. Spreadsheets drop leading zeros.
- Never reuse a SKU for a different product, even after the old one is discontinued.
- Don’t copy the supplier’s code or the UPC. If you change supplier, your SKU should stay the same.
Common SKU mistakes
- A different SKU on each marketplace for the same item. Stock can no longer be synced, and overselling follows.
- One SKU for several variations. You know you have 50 shirts but not which sizes.
- Letting marketplaces generate SKUs. Amazon creates a random SKU if you leave the field empty, and it cannot be edited later.
- Too many SKUs. Every extra variation adds stock to hold and picking errors. See how SKU proliferation increases picking errors.
Using SKUs across Amazon, Walmart, eBay and Shopify
Every channel has its own identifier: Amazon uses ASINs, Walmart uses item IDs, eBay uses item numbers. Your SKU is the one code that is the same everywhere, which is why multichannel software matches listings by SKU. Crazy Vendor’s inventory management keeps one stock count per SKU and updates Amazon, Walmart, eBay, Etsy and Shopify after every sale, and multichannel listings link each marketplace listing to the right SKU. Plans start at $29/month with a 21-day free trial. See pricing.
Related: a fast way to update SKUs and inventory forecasting.
Frequently asked questions
What does SKU mean?
SKU means stock keeping unit. It is a code a business assigns to each distinct product and variation it sells, used to track inventory and sales.
Is a SKU the same as a UPC?
No. A UPC is a universal barcode that is the same at every retailer. A SKU is created by each seller for internal use, so the same product has different SKUs at different companies.
Where do I find the SKU number on a package?
Many retailers print their SKU on the price tag, shelf label or receipt, usually labeled “SKU”. The barcode printed on the product itself is normally the UPC, not the SKU.
How long should a SKU be?
Short enough to read at a glance. 8 to 16 characters is a practical range for most catalogs.
Do I need SKUs to sell on Amazon?
Yes. Every Amazon offer has a seller SKU. If you don’t enter one, Amazon generates it for you, so it is better to set your own.
Updated November 12, 2026.