What is an ASIN? Amazon's product code and how it maps to an eBay listing

What is an ASIN?

What is an ASIN? It is the Amazon Standard Identification Number, which Amazon describes as a "unique 10-character alphanumeric code assigned to every product listed in the Amazon store". Most ASINs start with "B0", while those for books usually begin with a number. Amazon explains the format on its own guide to ASINs.

An ASIN identifies a product page, not a seller. Several sellers can offer the same product on one ASIN, at different prices, in new or used condition and with different delivery times. For an eBay seller who watches Amazon prices, that distinction matters: the ASIN tells you which product, and the offer on it tells you the price and delivery you are looking at right now.

Where do you find the ASIN on an Amazon page?

• In the product details. Scroll down the product page to the details or product information section, where the ASIN is listed with other facts such as dimensions.
• In the web address. Product URLs usually contain /dp/ followed by the ten characters of the ASIN.
• When you change options. If the product comes in several sizes or colours, each option you select has its own ASIN, and the code in the details and the URL changes as you click.

Always take the ASIN from the exact option you mean. Copying it from the first page you landed on is the most common way to link a listing to the wrong size or colour.

How is an ASIN different from a barcode, ISBN or SKU?

Products carry several codes, and each has a different owner and purpose:

eBay does not use ASINs. When eBay asks for a product identifier, it wants the barcode (EAN or UPC), the ISBN for books, or the brand and MPN. Our guide to eBay item specifics explains which fields matter in each category.

How does an ASIN map to an eBay listing?

The cleanest rule is one to one: each eBay listing, or each variation in a multi-variation listing, points to exactly one ASIN. That ASIN is the product page whose price, stock and delivery you track for that listing.

1. Record the ASIN in the custom label. eBay's custom label, or SKU, is a field you control. Putting the ASIN there, alone or inside your own code, lets you trace any listing back to its Amazon page.
2. Use the manufacturer's identifiers for eBay. Fill eBay's EAN, UPC, ISBN or MPN fields from the packaging or the manufacturer, so eBay can match your listing to its catalogue.
3. Map variations one by one. A size and colour on eBay maps to the ASIN for that exact size and colour, not to the parent page.
4. Keep the mapping when you edit. If you revise a listing, keep its custom label, so the link to the ASIN survives.

Tools that import products from Amazon work the same way. Dropizon can import products into eBay drafts from an Amazon product page or from a pasted list of ASINs, and each listing keeps the ASIN it came from. Our article on Amazon to eBay listing tools covers what to check after any import.

What does eBay's policy say about Amazon as a source?

Knowing the ASIN behind a listing does not change eBay's rules. eBay's drop shipping policy says that dropshipping from a wholesale supplier is allowed, but listing an item on eBay and then buying it from another retailer or marketplace that ships directly to your buyer is not allowed. The wording is on eBay UK's drop shipping page. Whatever your supply route, you stay responsible for delivery within the stated time and for the buyer's satisfaction.

Why can one ASIN show different prices?

Because an ASIN is a product page and not an offer, the price you see on it depends on which offer Amazon puts first and on where you are. The offer shown first is the buy box. It can change between sellers, between new and used, and between fast and slow delivery. Our guide to the Amazon buy box explains how that offer is chosen.

Location matters too. Amazon shows prices and delivery estimates for a delivery address, so two people looking at the same ASIN can see different delivery dates and sometimes different offers. When you track an ASIN, check it with the same delivery location each time, so changes reflect the product rather than your address.

Is an ASIN the same on every Amazon marketplace?

Often, but not always. A product can carry the same ASIN on amazon.co.uk and amazon.com, but that is not something to rely on. A product may exist on only one marketplace, have different options in each, or carry a different ASIN. Prices and currencies also differ. If you sell on more than one eBay site, check each ASIN on the Amazon marketplace in the same country.

Which ASIN mistakes cause problems on eBay?

• Parent instead of child. The parent ASIN of a product with options cannot be bought. A listing linked to it tracks nothing useful.
• Multipacks. A pack of 3 and a single unit usually have different ASINs. Linking a single-item listing to a multipack page doubles or triples the cost you track.
• Editions and versions. Books, games and electronics may have separate ASINs for each edition or model year. Match the one your listing describes.
• Duplicate pages. The same product sometimes appears under more than one ASIN. Pick one, record it, and stick with it.
• Changed pages. Amazon can merge, split or retire product pages. A link that worked last month may now point to something different, so recheck when tracking shows a sudden jump in price or a change in title.

Why do eBay sellers keep ASINs at all?

Sellers who use Amazon for price research, price history or stock checks keep ASINs because the code is the only stable link between an eBay listing and the Amazon page they compare it with. Titles change, photos change and search results shift, but the ASIN stays put. With the ASIN recorded, you can:

• check the current Amazon price of the product a listing is based on, without searching again;
• compare price history over weeks and months for the same product page;
• spot when a product goes out of stock or switches to used-only offers;
• trace a buyer's question or return back to the exact product details you listed from.

How do you keep an ASIN list organised?

A simple spreadsheet works until you have hundreds of listings. Give each row one eBay listing or variation, with these columns: eBay item number, custom label, ASIN, Amazon marketplace, the option values (size, colour, pack), the date you last checked the page, and notes.

Example (hypothetical): a seller lists a phone case in three colours. The spreadsheet has three rows, one per colour, each with its own ASIN, all on amazon.co.uk, all sharing one eBay item number but with different custom labels such as CASE-BLK-[ASIN]. When the red option's page stops showing a new offer, the seller knows at once which eBay variation to set to zero, because the row links the two. Without the ASIN in the row, the seller would have to work out from photos and titles which option was affected.

As the list grows, check rows on a schedule that puts your best sellers first, and mark rows you could not verify so they get a second look.

A checklist for linking ASINs to eBay listings

• Take the ASIN from the exact size, colour and pack you are listing.
• Store it in the eBay custom label for every listing and every variation.
• Use the barcode, ISBN or MPN, not the ASIN, for eBay's product identifiers.
• Track each ASIN with the same delivery location and on the right Amazon marketplace.
• Recheck a mapping whenever its price or title changes sharply.