Labels, Barcodes, Numbers, and Codes — What They Are and Where and Why You Need Them

What do all those numbers and codes mean, anyway? Let’s find out.

Sandi & I have been in retail since – well, I don’t know when.

We had our own shop from 1971 to 1989. Sandi managed card shops all along the West Coast from 1985 until 2002. We both worked for retailers while in and after high school.

I guess we’ve had what you’d call “experience”.

Because of that, Amazon didn’t present much of an understanding leap for us when it came to labels, codes, and numbers for our products.

Unless you’ve had some sort of exposure to the retail world, those ASIN, SKU, UPC, ISBN, EAN, and FNSKUs can overwhelm. Especially when it comes to prepping your products for shipment.

Let’s define the codes and numbers you need to keep track of.

UPC – Universal Product Code. That’s the barcode your store cashier scans for the price.

ISBN – International Standard Book Number

ASIN – Amazon Standard Identification Number

SKU – Stock Keeping Unit – used interchangeably with MSKU.

MSKU – Merchant Stock Keeping Unit – used interchangeably with SKU.

FNSKU – Fulfillment Network Stock Keeping Unit

GTIN – Global Trade Item Number

EAN – European Article Number (This is nearly identical to the UPC with an additional number at the beginning.)

When you are Finding your products by scanning around the house or at retail stores, you are scanning the UPC or ISBN barcode They have a specific format that was developed to let laser scanners at cash registers and in inventory control identify the item. The number is in tiny numbers along the bottom of the barcode, and it includes ALL the numbers, even the tiny ones on each end.

The ISBN barcode, although different from a UPC code, uses a similar layout. It, too, includes ALL the numbers.

In the USA, you’ll generally find UPCs and ISBNs.

WARNING! Some stores use their own unique barcode for their inventory. Their cash registers are programmed for those numbers. They are not valid for Amazon purposes. Big Lots is one example.

Let’s follow a typical Find It, List It, Ship It process to see how these all fit together.

Using the free Amazon Seller app on your phone, you scan a product. It thinks for a bit, then displays a product already listed on Amazon. It used the UPC code to find the item in Amazon’s catalog. The UPC (or ISBN) is Required information when listing on Amazon. (There are exceptions, but we won’t cover them here.)

When a listing is created, Amazon requires the UPC NUMBER, not barcode, to list.

You enter this and that information until you come to the SKU field. This is YOUR field. You can put whatever information about this product that you want (except spaces). It is just for you. The customer will never see it. This is displayed when you Manage your Inventory. If you don’t put something here, Amazon will assign some random number/letter combination that will mean nothing to anybody except Amazon.

What should you put there?

Sellers regularly put the Source, Order #, and Cost. I do Source-Brief Description, and Order #.

You should think about what information (this is called META-data) you’d like to know whenever this number is displayed. It will show in many reports, in your Manage Inventory and related pages, etc.

Those are the only specific numbers you need to List a product.

When you Save your entry, Amazon will assign the ASIN to this UPC/Product. (Existing listings already have an ASIN assigned to them.)

Each listing only has ONE UPC, and ONE ASIN. Once created, that UPC and ASIN Can’t be changed. Each listing can have multiple Sellers. Each will have their own SKU and FNSKU.

It will also assign an FNSKU number to it. If you are creating an FBA listing, you will be asked if you will want a Manufacturer’s or Amazon barcode.

If you choose Manufacturer’s barcode, the FNSKU will begin with the latter “B” (at least for me it does.) If you choose Amazon barcode, it will begin with an “X”.

Which should you choose?

If you choose Manufacturer’s barcode, when it comes to prep time, you can just leave the UPC barcode exposed. This will also put your specific inventory “co-mingled” with every other Seller of this item who chose Manufacturer’s barcode.

The joy is one less step in prep. The downside is that when a customer buys from “you”, they might get “their” version, and who knows how good that prep has been.

When we’ve requested Amazon to remove some of our inventory and send it back to us, we get items definitely not “ours”. Same product, just not the ones we sent in.

If you choose Amazon Barcode, your item will be assigned a unique FNSKU, and it will not be co-mingled with anybody else’s inventory.

The downside? Every one of the items will require a new label during prep.


Every Listing requires a UPC NUMBER, not barcode. If it is an existing listing, that UPC has already been entered.

Every Item sent to FBA requires a barcode. Depending on how you elected labels, it might be the existing UPC barcode, or a new label with your FNSKU barcode.

(Merchant Fulfilled can have any barcode you want. However, you can’t print Labels for Merchant Fulfilled from your Manage Inventory page.)

Questions? Just let me know.

John L

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