A guide on SKU codes

Last update June 5, 2023

SKU codes

What they are, how to pick them for e-commerce, how to use them on marketplaces

In this guide, we will teach you what SKU codes are, how to use them for your online business, and we will give you some advice on how to pick the best SKU. Following, we are going through five different marketplaces and e-commerce channels, their rules for SKUs, and some best practices.

A guide from Nembol.

What is an SKU code

SKU stands for “Stock Keeping Unit”, a concept born to define the single picking item in a warehouse system.

In a consumer-goods setting, such as most b2c businesses reading this article, it is the single product a seller can sell and ship. For instance a specific shoe model, in a specific size, in a specific color variation.

The SKU is therefore a single unique item, and the SKU code, as a consequence, is a unique code assigned to it.

This means that in a good design e-commerce setting, SKU codes should be unique, never repeated. And some e-commerce system will force you to behave.

For instance, WooCommerce does not allow you to assign the same SKU code to different products, or different variations in the same WooCommerce Store. It will simply not save the information if you try in your WordPress / WooCommerce backend, and it will return an error “Duplicated variation” if you tried via Nembol.

Read more: Amazon SKUs and barcodes while listing new products

What is the difference between an SKU code and a Barcode?

Both an SKU code and a barcode are uniquely assigned to a pickable item, so why do I need both?
There’s a bunch of reasons:

1. Barcodes (or GTINs) such a UPC, EAN, or ISBN are centrally defined and reflect an international standard.
   Amazon requires you to purchase them from GS1 for instance, so you cannot pick or self-define your UPC or EAN barcodes
2. SKU codes are self-defined by each business. So each industrial manufacturer defines its SKU codes, and we strongly advise retailers to stick to those.
3. SKU codes are typically “speaking”, meaning that since I can self-define them for my business, I will have the SKU-code to be readable by a human.
   Example: for a jacket, size M, color black, season Fall Winter 2020, I may pick: JKT-M-BL-FW20. If I have more jackets in my catalog, I will add their name or model or style, for instance, “Brag jacket” could be BRG-JKT-M-BL-FW20.

So SKU codes can be of any size and format. We though advise as following.

Read more: Amazon categories, barcodes and SKUs

Good advice on how to pick an SKU code set

1. Use the manufacturer’s assigned SKU codes unless forced otherwise (it’s hard to foresee something forcing us to move elsewhere).
2. Keep them as simple and short as possible.
3. Let them start with a letter or number, because some e-commerce system will block you otherwise.
4. Avoid using the letters “O” and “I”, and lowercase “L”. They can easily be mistaken for numbers or one another.
5. Avoid using symbols, like commas, semi-columns, or slashes. They may mess you up on some spreadsheets programs.
6. Use SKU codes consistently with the GTIN (aka barcode, UPC, EAN, ISBN) originally associated with it.
7. In most cases, you may use a barcode as an SKU code, but not vice-versa.

SKU codes for Marketplaces and e-Commerce

Now let’s see all constraints imposed on SKU code choice and use by today’s main e-commerce systems (and those connected to Nembol)

SKU codes on WooCommerce

• You can use any combination of letters an number, as long as it is unique across your WooCommerce store;
• You must assign SKU codes for products with variants.

SKU codes on Amazon

• SKU codes are required by Amazon. This means that any product listed to Amazon MUST have an SKU code associated, exactly as it must have a brand. This is true also if you are barcode exempted;
• SKU code and barcode association on Amazon must be consistent.
  I.e. if some other seller made a wrong or different association between a GTIN and an SKU code, your listing attempt will be rejected by Amazon and you will have to appeal to Amazon seller support.

SKU codes on eBay

• SKU codes are not required by eBay;
• Nembol will generate random SKU-codes to listings imported from eBay to Nembol which are lacking SKU codes in the first place.

SKU codes on Etsy

• Etsy requires your SKU codes to start with either a letter or a number. If you attempt to list an SKU with a differing SKU code, Etsy will return the error “SKU code does not start with letter or number” and reject your listing attempt;
• Max length for SKU codes is 32 characters on Etsy;
• Here’s an article on Etsy blog giving some further advise

SKU codes on Shopify

• No constraints from Shopify as often happens;
• Here’s a good support article in Shopify blog on how to use SKU codes.

How to edit or add SKU codes inside Nembol for all channels

Just edit a product, scroll down till you see the SKU code field, paste or type the correct SKU code in it. See screenshot.

How to add or edit SKU codes for all marketplaces in Nembol

Just edit a product in Nembol, scroll down till you see the SKU code field (or the variation section if the product has variants) type or paste in the SKU code field the correct SKU code, click save.

If the product is already listed, Nembol will edit each listing addingor correcting the SKU code.