Paste FNSKUs (one per line, optional title after a comma) and download a print-ready PDF — sized to the millimetre for label sheets and thermal rolls, so what comes out of the printer actually scans at the fulfilment centre.

FNSKU vs UPC — which barcode goes on the unit?

The UPC/EAN on your packaging identifies the product and belongs to the manufacturer’s numbering. The FNSKU identifies your inventory of that product inside Amazon’s warehouses. When a unit needs an Amazon barcode, the FNSKU label must completely cover every other barcode on the box (serial-number barcodes such as IMEIs are the one exception) — otherwise a scanner may pick up the wrong code at receive.

Amazon-assigned FNSKUs start with X00; when your FNSKU equals the ASIN it starts with B0. Both are real — this tool accepts both and warns on anything else, because a seller SKU pasted into the FNSKU column is the classic way to print a batch of useless labels.

Labels required for more sellers from 2026

Amazon is ending commingled inventory (announced at Amazon Accelerate 2025). Per Amazon’s Seller Central announcement — as consistently reported across the industry — shipments arriving from 31 March 2026 must carry an FNSKU label on every unit unless a Brand-Registry-enrolled brand owner uses the manufacturer barcode. The date itself sits behind the Seller Central login, so we cite it at that evidence level rather than linking a page you could not open.

Why “exact size” is the whole product

A Code 128 barcode survives printing when its narrowest bar is a whole number of printer dots. This tool asks which printer family you are using and lays the bars on that dot grid — then sizes the PDF so 1 inch in the file is 1 inch on paper. The one thing that silently breaks this is the print dialog’s fit to page setting, which is why the calibration page exists: print it, put a ruler on it, and if 1″ doesn’t measure 25.4 mm you know exactly what to fix before wasting a sheet of labels.

Label stock, per Amazon’s own guide

Black ink on white, non-reflective labels with removable adhesive; laser or thermal printers (inkjet smudges are explicitly out); the label must stay scannable for 24 months. Sizes from 1″ × 2″ up to 2″ × 3″ are accepted — every format this tool offers stays inside that window.

Every check this tool runs (12 rules)

LBL-F01 Empty input

There is nothing to encode. Each label needs one FNSKU.

Fix: Paste the FNSKU from Seller Central (Manage Inventory → FNSKU column).

Source: Amazon Seller Central Help → "FBA product barcode requirements" (help ID G201100910) and "Use an Amazon barcode to track inventory" (help ID G200141490). Seller Central requires a seller login, so we describe the source rather than linking to a page that would show you the homepage; the same content is available in Amazon's public PDF "Use an Amazon barcode to track inventory" (linked where this rule cites it).

LBL-F02 Not 10 characters

FNSKUs are 10 characters. 12–13 digit inputs are usually a UPC/EAN pasted into the wrong column — an FBA label with the manufacturer barcode on it defeats its purpose.

Fix: Copy the FNSKU exactly as Seller Central shows it.

LBL-F03 Lowercase letters

FNSKUs are uppercase. A lowercase letter scans as a different Code 128 value, so the printed label would point at a different (usually nonexistent) inventory item.

Fix: Re-copy from Seller Central rather than uppercasing by hand, in case other characters were mangled too.

Source: Amazon publishes no formal FNSKU grammar. The 10-character length and X00/B0 prefixes are industry consensus corroborated by Amazon's own label illustration (FNSKU example X00009377F in the official 2016 labeling guide) and by B0-prefixed FNSKUs equal to the ASIN in manufacturer-barcode scenarios.

LBL-F04 Characters outside A–Z / 0–9

FNSKUs contain only letters and digits. Punctuation usually means a spreadsheet export added quoting or a column shifted.

Fix: Check the source row; strip stray punctuation.

LBL-F05 Unusual prefix

Amazon-assigned FNSKUs start with X00; when the FNSKU equals the ASIN it starts with B0 (both forms are real — the "always X00" rule of thumb is community consensus, not official documentation). Anything else is usually a merchant SKU.

Fix: Confirm the value came from the FNSKU column, not the SKU column.

LBL-B01 X-dimension at the 2-dot floor

On this label size and printer density the barcode narrow bar had to be pinned to the minimum of 2 printer dots. It should still scan, but tolerances are tighter.

Fix: Scan-test the first printed label; if it fails, use a larger label size or a 300 dpi printer.

Source: This is a rule of this tool's print engine, not an Amazon requirement — stated so you can see exactly what the tool does.

LBL-P01 Print at 100% — never "fit to page"

The PDF is laid out at exact physical size; any scaling changes the bar widths and the label grid. Amazon's own instructions say to set print scaling to "None".

Fix: In the print dialog choose "Actual size" / 100%. Use the calibration page to verify.

Source: Amazon (official PDF) — Use an Amazon barcode to track inventory

LBL-P02 300 dpi recommended

Amazon recommends printing barcodes at 300 dpi or higher. 203 dpi thermal printers are common practice and this tool aligns bars to their dot grid, but 300 dpi has more margin.

Fix: If your thermal printer supports 300 dpi, pick the 300 dpi option.

Source: Amazon (official PDF) — Use an Amazon barcode to track inventory

LBL-T01 Title characters replaced for print

The label is printed with a standard PDF font that covers Western (WinAnsi) characters only. Characters outside it (CJK, emoji, exotic punctuation) were replaced or dropped — the change is listed, never silent.

Fix: Shorten the title to its Latin part, or accept the replacement — the title line is informational; the barcode is what Amazon scans.

Source: This is a rule of this tool's print engine, not an Amazon requirement — stated so you can see exactly what the tool does.

LBL-T02 Title truncated to fit

Long titles are cut with an ellipsis so they never overlap the barcode.

Source: This is a rule of this tool's print engine, not an Amazon requirement — stated so you can see exactly what the tool does.

LBL-C01 Cover every other barcode

The FBA label must completely cover all other barcodes on the packaging (manufacturer UPC/EAN/ISBN). Exception: serial-number barcodes such as phone IMEIs stay visible.

Source: Amazon (official PDF) — Use an Amazon barcode to track inventory

LBL-M01 Label stock requirements

Black ink on white, non-reflective labels with removable adhesive; laser or thermal printers (no inkjet); must stay scannable for 24 months. Place labels on a flat surface, ≥6 mm from any edge.

Source: Amazon (official PDF) — Use an Amazon barcode to track inventory

Sizing, coverage and stock rules cite Amazon's public barcode guide (PDF). The FNSKU format itself has no official public grammar — those checks are labelled as industry consensus corroborated by Amazon's own label illustrations, not as official rules.

FNSKU Label Generator

FNSKU vs UPC — which barcode goes on the unit?

Labels required for more sellers from 2026

Why “exact size” is the whole product

Label stock, per Amazon’s own guide

Every check this tool runs (12 rules)

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