Last updated June 2026
Clear answers to common barcode and Amazon FBA questions. No ticket queues. Just straight fixes you can apply right now.
If you're in the warehouse and need the right next step, use one of these.
FNSKU stands for Fulfilment Network Stock Keeping Unit. It's an Amazon-assigned code that links a specific product variation to your seller account. Find it in Seller Central: Manage Inventory → select your product → Print Item Labels. It starts with X00 and is 10 characters long (e.g., X00ABC123D).
For most FBA sellers: you need the FNSKU on the physical item. The EAN/UPC is used to create your Amazon listing, but the FNSKU is what goes on the label applied to the product before it reaches the fulfilment centre. The only exception is if Amazon has granted you a manufacturer barcode exemption. See our FNSKU vs UPC vs EAN guide.
Amazon FNSKUs use the Code-128 barcode format. Our generator produces Code-128 by default when you select "Code-128 (Amazon FNSKU)" from the type dropdown. EAN-13 and UPC-A use their respective linear barcode formats. The 2D box content label uses PDF417 format.
A PDF417 barcode label that tells Amazon exactly what's in a carton before they open it — including the Shipment ID, FNSKUs, and quantities. Required on all inbound FBA cartons since 2024. Build one free with our 2D Box Content Builder.
Screen scanning isn't a reliable test — screen pixels simulate bars but don't reproduce print quality. Common print issues: scale not set to 100%, DPI too low, inkjet using colour mode instead of black-only, or glossy paper causing glare. See our full print guide.
Minimum 300 DPI for reliable scanning. At 203 DPI (thermal printer minimum) you'll get readable results, but they're borderline in poor lighting. For inkjet printers, use 600 DPI if available. Always test-scan from the physical print before applying to stock.
Check two things: (1) the barcode image itself — is it created at the correct physical dimensions (e.g., 2 inches wide)? (2) the label template — is the image container in your Word or Avery template set to the correct size? Sometimes the image is correct but the container is resizing it. Check the image properties in your layout software to confirm the exact dimensions in inches or millimetres.
Standard FNSKU item label: 1 inch × 2 inches (25.4 × 50.8mm). Alternative: 1 inch × 3 inches (25.4 × 76.2mm). Both are acceptable. The 2×1 inch size fits on most products without crowding. Quiet zone: 2.5mm minimum on all sides of the barcode.
The PDF417 2D box content label should be 4 inches × 2 inches (100mm × 50mm) as a minimum. Our 2D Box Content Builder generates it at exactly 100×50mm at 300 DPI — the correct size for Amazon FBA inbound shipments. Place on the side of the carton only, not the top or bottom.
The quiet zone is the mandatory clear white border around a barcode. For FNSKU labels: 2.5mm minimum on all sides. For 2D box labels: 6mm minimum. Without an adequate quiet zone, scanners can't find the barcode boundaries. Our generator includes the correct quiet zone automatically in all downloads.
Most common causes: wrong print scale (use 100%/Actual Size), DPI too low, manufacturer barcode visible under the FNSKU label, label on a seam or curved surface, packing tape over the barcode, or missing 2D box content label. See the full rejection guide for all causes and fixes.
Typically £0.15–£0.20 per unit in the UK, $0.15–$0.30 per unit in the US, depending on the nature of the problem. For a 500-unit shipment with labelling issues, that's £75–£100 in unexpected fees on top of the delay.
Yes. Shiny packing tape creates glare under Amazon's infrared scanners. The reflected light interferes with reading the dark bars. Never cover a barcode with tape — not even clear tape. If you need to secure a label edge, apply tape around the label, not over it.
Check: (1) For EAN-13, you need exactly 13 digits. (2) For UPC-A, exactly 12 digits. (3) For Code-128 (FNSKU), any length is accepted — but verify it starts with X00. The validator message below the input field will tell you exactly what's wrong.
SVG is vector-based and scales to any size without losing quality. It's the best choice for printing. PNG is a raster image at a fixed resolution — fine for most uses, but may appear slightly pixelated if scaled up significantly. For QR codes, only PNG is available.
Check: (1) Shipment ID is filled in with no commas or special characters. (2) At least one ID + Qty row is complete. (3) If using expiry date, it must be exactly 6 digits in YYMMDD format (e.g., 251231 for 31 Dec 2025). The error message in the preview panel will tell you specifically what needs fixing.
No data leaves your device. All barcode generation and 2D label building runs entirely in your browser using JavaScript. Your FNSKU codes, Shipment IDs, and inventory data are never sent to any server — ours or anyone else's. This is by design, not just a policy promise. You can verify by checking your browser's network tab — you'll see zero outbound requests when generating barcodes.
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