Codes
FNSKU vs UPC vs ASIN
A UPC identifies a product everywhere (12 digits, from GS1). An ASIN identifies a product page on Amazon (10 characters, usually starting B0). An FNSKU identifies your units of that product in Amazon’s warehouses (10 characters, usually starting X00). For FBA you print the FNSKU, unless your listing is set to use the manufacturer barcode. For Walmart WFS you print the UPC or GTIN.
| UPC / EAN / GTIN | ASIN | FNSKU | |
|---|---|---|---|
| Looks like | 036000291452 | B07XYZ1234 | X002QK8V1N |
| Who issues it | GS1 (the brand buys it) | Amazon, per product page | Amazon, per seller and product |
| Identifies | The product, in any store | The product page on Amazon | Your units in FBA warehouses |
| Barcode type | UPC-A / EAN-13 (or GS1-128 for GTIN-14) | Not printed as a barcode | Code 128 |
| Check digit | Yes, last digit | No | No |
| On an FBA label | Only with manufacturer-barcode listings | No | Yes |
| On a Walmart WFS label | Yes (UPC-12 or GTIN-14) | No | No |
Why FBA uses FNSKUs
Many sellers can sell the same UPC. An FNSKU ties each unit to the seller who sent it, so Amazon knows whose stock it is. Until 2026 resellers could skip it and let Amazon pool identical units (commingling). Since March 31, 2026, resellers without brand registry need an FNSKU on every unit.
When an FNSKU starts with B0
If Amazon tracks your item by its ASIN, the FNSKU on the label is the ASIN itself. That’s normal; Prepline accepts both X00… and B0… codes and flags anything else that’s 10 characters long.
Telling them apart in a spreadsheet
- 12 digits with a valid check digit: UPC. 13 digits: EAN. 14: GTIN-14.
- 11 digits: almost always a UPC that lost its leading zero in Excel. Prepline adds it back when the check digit confirms it.
- Something like
3.60003E+11: Excel turned it into scientific notation and the digits are gone. Format the column as Text and export again.
Questions
Is the FNSKU the same as the UPC?
No. The UPC identifies the product in any store; the FNSKU identifies your units of it in Amazon’s warehouses. For FBA you normally print the FNSKU.
Can the FNSKU be the same as the ASIN?
Yes. When Amazon tracks your item by its ASIN, the FNSKU shown is the ASIN, starting with B0.
What barcode type is an FNSKU?
Code 128. UPCs use UPC-A, EANs use EAN-13.
Updated November 9, 2026