Overview
Barcode numbers that fail validation or scanning typically fall into two distinct categories: numeric validity errors (the data itself is wrong) and physical scannability issues (the symbol is damaged or poorly printed). This guide covers the most common failures in each category and how to resolve them.
Numeric validity errors
These occur when the GTIN itself is malformed, incorrect, or already assigned elsewhere. A validator such as the check digit calculator or the GTIN validator can help find malformed and incorrect numbers.
Verfier services such as IBN Verified and Verified by GS1 can help you identify whether a GTIN number has already been assigned for use on a product. When you have a pool of numbers assigned to you for use on your own products, it pays to keep a master record of which GTINs you have assigned to which products. This could be as simple as paper records or a spreadsheet, or as complex as an internal database of your own. Using a barcode registration service such as IBN’s Barcode Registration can offload the burden of remembering which-products-use-which-GTINs to a third party, especially useful if your local records are lost, damaged, or corrupted.
| Error | Typical cause | Quick fix |
|---|---|---|
| Wrong check digit | Manual entry typo; spreadsheet formula error | Recalculate using a check digit calculator; verify the final digit |
| Wrong length | UPC-A (12 digits) entered as EAN-13 (13 digits); GTIN-8 vs GTIN-13 confusion | Confirm the required format for the target market and packaging size |
| Missing leading zero | UPC-A converted to EAN-13 by prefixing 0, but the zero was dropped in data entry | Ensure GTIN-14, GTIN-13, and GTIN-12 fields preserve leading zeros in databases |
| Reused GTIN | Same number assigned to multiple SKUs; recycled from discontinued product | Check internal master data; verify against your product database before assignment |
Check digit failures in detail
The check digit is calculated from the preceding digits using a weighted modulo-10 algorithm. A single transposed digit or wrong final digit will fail validation.
- EAN-13 / GTIN-13: 13 digits, check digit at position 13
- UPC-A / GTIN-12: 12 digits, check digit at position 12
- GTIN-14: 14 digits, check digit at position 14
Always validate the full digit sequence before sending product packaging artwork to print.
Leading zero truncation
Spreadsheets, data input forms, and some databases, may strip leading zeros from numeric input fields. Consider a valid GTIN-12 of 012345678905 being entered into a truncating input field, it becomes 12345678905 (11 digits) and fails length validation. Be careful when storing GTINs, make sure to store them as text strings, not integer numbers, to ensure leading zeroes are not truncated.
Scannability vs. numeric validity
A GTIN can be mathematically valid yet physically unscannable. It is paramount to ensure and verify one’s product packaging has good print quality less they run the risk of unscannability. These are separate verification stages:
| Stage | What it checks | Tool or method |
|---|---|---|
| Numeric validation | Correct digits, length, check digit | GTIN validator, manual calculation |
| Physical scannability | Symbol contrast, quiet zone, print quality, damage | Scanner test, consider Barcode Philipine’s colour legibility simulator as a lightweight check, ISO/IEC verification, verification reports |
Never skip physical testing. A valid GTIN can still fail scanning due to the colors used in printing. Variable lighting conditions and scanner head technologies can even cause barcodes to scan some of the time, consider that a barcode printed in yellow on white may scan in perfect lighting but fail in a warehouse. GS1 guidance on symbol placement and print quality is available in GS1 UK’s barcoding guide and GS1 US symbol placement guidelines.
When in doubt, the gold standard for barcode coloring remains black bars on a white background for maximum contrast. The black on white won’t interfere with red light laser scanners not optical scanning systems.
Common physical scanning failures
Insufficient quiet zone
The quiet zone is the blank margin on either side of the barcode. Without adequate space, the scanner cannot distinguish where the barcode symbol begins and ends.
- EAN-13 / UPC-A: minimum 3 modules (≈ 2.31 mm at 100% magnification) on left and right
- Quiet zone violations often occur when artwork crops the barcode too tightly or places text or graphics adjacent to the bars
See packaging artwork checks for design-stage prevention.
Poor colour contrast
Barcodes require high contrast between bars and background. The ideal combination is black bars on a white background. Common failures include:
- Red, orange, or light brown bars (scanners will commonly read red light; these bar colors reflect red light back to the scanner instead of absorbing it like black bars do, making the bars appear as background to the scanner)
- Reversed-out (white bars on dark background) without proper verification
- Metallic or reflective backgrounds causing specular reflection
The barcode colour legibility simulator previews how different colour combinations perform under scanner illumination. For peace of mind one may consider purchasing barcode verification testing from a vendor, where their product packaging is physically tested for scannability.
Print quality defects
| Defect | Effect on scanning | Typical source |
|---|---|---|
| Bar growth / spread | Bars wider than spec, spaces narrow | Ink bleed on absorbent substrates |
| Bar loss / voids | Bars thinner than spec, breaks in lines | Low ink density, plate wear |
| Spot noise | False edges in quiet zone or spaces | Dirty print environment, poor substrate |
| Incorrect magnification | Symbol too small for scanner resolution, fuzzy bars | Scaling artwork size without proportion control, increasing the scale of raster graphic artwork |
For detailed EAN-13-specific issues, see EAN-13 barcode scanning issues and fixes.
Recommended troubleshooting workflow
When a barcode is rejected or fails to scan:
- Validate the number first — Use a GTIN validator to confirm length, format, and check digit
- Test the physical symbol — Scan with multiple devices (laser, imager, smartphone) in realistic lighting
- Inspect quiet zone and colour — Compare against scanner compatibility requirements and run through the colour legibility simulator
- Verify print quality — If mass production, request ISO/IEC 15416 or 15415 verification from your printer
- Check for reuse — Query your internal product database for duplicate assignments
Prevention checklist
- Store all GTINs as text, not numbers, to preserve leading zeros
- Validate every new number before artwork creation
- Maintain a central registry to prevent GTIN reuse
- Require physical scan testing on production samples
- Review artwork against quiet zone and colour contrast rules before print approval