5 tricks to master the Amazon Seller Sku or MSKU

Travis R.
Amazon seller & Software Founder

When you’re selling on Amazon it can be really hard to manage all of the moving parts to your business.  There are all sorts of new terms you have to recognize and understand their meaning.

There is the MSKU, the ASIN, FNSKU, the UPC number, purchase orders and the ever elusive Inventory Health metric

It can be very overwhelming.

After all, you got into this Amazon business because you heard it was relatively easy, right?

Shop and source for products to sell, list them and ship them into Amazon’s warehouse and they do the rest, right?

Of course!

“Easy to make money” is why Amazon is bringing on over 100,000 new sellers every year.  But in order to really be successful you will inevitably need the right tools and a pinch of 📚 education to make any serious money in the Amazon ecosystem.

Whether you’re doing Retail Arbitrage (RA), Online Arbitrage (OA) or Private Label (PL), the first place where you can employ some systems to help your business is going to be in the SKU of your product.

What is an Amazon seller sku or MSKU?

An Amazon seller sku  is a unique string of letters and numbers that a 3rd party seller assigns to their product in order to keep track of it.  The seller sku is all about the tracking.

seller msku

But the seller sku or MSKU is one of the last strings of text you will find assigned to any product being sold on the Amazon marketplace.  

Any product usually starts out with a UPC code and then gets an ASIN and then gets a MSKU and then a FNSKU

What is a UPC code?

A UPC code stands for “Universal Product Code” and it’s assigned to products by the manufacturers who make those products.  It’s a widely accepted form of tracking and registration system adopted by most countries across the globe.

anatomy of a book barcode

More specifically, it’s a barcode symbol encoding a 12-digit number called a GTIN-12.  The GTIN-12 is essentially the UPC data derived primarily from a GS1 Company Prefix and Item Reference Numbers

What is an Amazon ASIN?

For any physical item in the Amazon catalog, Amazon creates and attaches an ASIN number to it.  But that is NOT the seller sku.

An ASIN number stands for Amazon Stock Identifier Number and it’s their own unique identifying number that allows them to catalog all the products they sell. Think billions of products.


You won’t have to worry about the Amazon ASIN number at all because Amazon assigns that to all physical products but you will need to create and manage your seller sku or MSKU for every product you ship into the Amazon warehouse.

What is an Amazon MSKU?

The MSKU or seller sku is an acronym for Merchant Stock Keeping Unit.

It’s literally the fancy shmancy number you assign a product that you are selling on Amazon.

An example of an MSKU could be something like this:


To the customer buying the product it’s just a bunch of numbers, letters and symbols but to the seller it’s holding a lot of knowledge about the product.

What is an Amazon FNSKU?

Often sellers get the MSKU and FNSKU mixed up.  If you sell on Amazon FBA then  you will have both assigned to your products you are selling.

That is because an MSKU identifies your product and an FNSKU identifies your product versus all of the other sellers who sell the same product inside the Amazon fulfillment centers.

Here is an example of an FNSKU label that would go on a sellers product and be sent into the Amazon warehouse:

fnsku example1

Why do you have to manage the Amazon seller sku?

If you send in a popular book to be sold by Amazon then chances are that other sellers are sending in that very book to be sold too.  So you’ll need your own seller sku or FNSKU in order to properly identify your book against the many other seller’s books in the warehouse.

This is not only for proper inventory control but also how Amazon knows they have sold YOUR book and not your competitor’s book.

Time to get paid! 💰Cha Ching!

Below is a great example of a bad MSKU and a good MSKU.  Do you notice the difference in structure between the two?

The Multiples are insane

Just thinking about how many products Amazon has in their complete catalog is daunting.  Just thinking about how much inventory you may have can be daunting as well.  One of the best ways to manage that inventory and give you valuable sales insight is to leverage a custom seller sku.

You are already tasked with creating a sku for each one of your products so why not make that seller sku work for you?  Knowing certain information about your products each and every time you sell it will help guide you as you set out to source more goods.

We’ve compiled some of the best tricks and tips for your custom seller sku below.  For purpose of illustration, we’ll use the following custom sku and break it down piece by piece to explain its purpose:

5 ways to own your custom seller sku

Source Identifier:

When you’re doing RA or OA, it’s very important to keep track of where your products are coming from.  If you see things flying out the door that you got from Craigslist (CL) and all of the items you got from Walmart (WM) are collecting then where will you most likely keep sourcing from?   Craigslist.  So it’s nice to know with each sale, where are you getting those items?

Product Identifier:

OK so common sense might have you wondering why would I need to describe the item I am selling when I can clearly see a picture of it on the Seller Central app or website?  Well, in a lot of cases, the picture isn’t always clear as to what the item exactly is.  

A cover photo of a book can look a lot like the front of a CD and vice versa.  If you see a lot of CD descriptors in your item sales, then you’ll know immediately without looking at the picture that you’re selling a bunch of CDs and maybe it’s time to source some more.

Date Identifier:

We happen to think this is one of the most important ways you can customize your Amazon seller sku.  If it’s April and you see a bunch of items selling that were sent in last November, then you can immediately identify some trends either within that product or trends associated to the timing of the sale.  

Did you buy Spring clothes in November to be sold starting in April?  Guess what, your custom seller sku just validated your selling strategy.  Powerful huh?

Condition Identifier:

This one is important too because knowing the velocity of sales relative to the condition of the product is important for future sourcing trips.  Are items in NEW condition selling better than used?  Ok maybe it’s time to source differently and stock up on NEW products instead of other conditions.

Buy Cost Identifier:

This isn’t absolutely critical to your business because you already know exactly how much you paid for the item when you sourced but it could put a smile on our face every time you sell a CD for $10+ and your sku says you bought it for $.50 cents.  Oh yeah!!!

AccelerList makes it easy

If you want a super fast Amazon product listing application to help you build custom skus then you might want to try us out.  We make building your custom sku a very easy process.  Just select any of our pre-made tags or create your own custom one.

custom sku blue tags

Putting it all together

The last digit on the custom seller sku is the actual # of the product within the batch.  So for the example sku above, this would be the 4th item in the box as we ship it in.

As your business grows these custom skus will mean even more and get even more precise.

For example, if you have hired remote employees to help you find and source product then you could incorporate their names within the sku.

No matter what system you set up for your business, custom skus can be executed as an inventory strategy at any size.

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