Why won't my barcode scan? 11 causes and how to fix each one
First, decide which problem you have. If the scanner beeps but the till says "item not found", the barcode is fine and the number isn't in that shop's system. If nothing happens at all, the scanner can't read the barcode. This guide is about the second case, starting with the most common causes.
1. The quiet zone is missing
Text, a border or the edge of the label sits too close to the bars. Scanners need clear space on both sides to find the start and end. Leave at least 10 module widths, or the GS1 amounts for retail codes (11 left and 7 right on an EAN-13).
2. The barcode is too small or cut short
Retail barcodes below 80% of their standard size, or with the bars cut short to fit, are hard to read. Logistics barcodes need a much larger module than retail ones: at least 0.495 mm for ITF-14 and GS1-128 on cartons. See barcode print size and quiet zone.
3. The colours don't work for the scanner
Laser and LED scanners use red light. Red, orange, yellow and light brown bars reflect it and become invisible, and a red background makes black bars hard to see. Use black or dark blue bars on white. Bars on a transparent label over a dark product are another common failure.
4. The image was stretched or blurred
A small PNG enlarged in a design program gets soft edges and uneven bars. Download at your printer's resolution and place it at 100%, or use a vector file. Never stretch a barcode in one direction only.
5. Bars printed too thick or too thin
Ink spreads on absorbent paper and corrugated board, which fattens the bars and narrows the spaces. Thermal printers with worn heads leave white lines through the bars. Ask the print shop about bar width reduction, and replace or clean worn print heads.
6. The module width doesn't match the printer
On a 203 dpi printer, a 0.33 mm module can't be printed evenly, so some bars come out wider than others. Pick a whole number of printer dots, such as 0.25 mm or 0.375 mm.
7. The scanner has that barcode type switched off
Many scanners ship with only the common types switched on. Codabar, Code 39, ITF and the 2D codes are often off by default, and ITF scanners are often set to accept only certain lengths to avoid partial reads. Check the scanner's setup guide; most are configured by scanning setting barcodes printed in the manual.
8. The scanner can't read 2D codes
Data Matrix, PDF417, Aztec and QR codes need a camera-based imager. Older laser scanners only read linear barcodes. Many phone camera apps only look for QR codes, so test with a barcode scanner app instead.
9. The check digit or content is wrong
An EAN or UPC with a wrong check digit won't be accepted by the scanner at all. Code 39 can't hold lowercase letters, and GS1-128 needs correct Application Identifiers. Our generator checks all of this and test-scans every barcode, so a file downloaded from it always decodes.
10. The surface gets in the way
Glossy film reflects the scanner light, curved bottles bend the bars out of view, and barcodes over seams, folds or corrugation flutes break up. Use a matte finish where you can, turn barcodes on narrow cylinders so the bars run horizontally, and keep them on flat panels.
11. Damage and wear
Scratches, scuffs and water damage break the bars. Linear barcodes have no error correction, so a scratch across the full height can stop the scan. Taller bars, lamination for labels that get handled, and Data Matrix for parts that wear all help.
A quick way to find the cause
- Scan the file on screen. If the digital file won't scan, the problem is the barcode itself: the number, the type or the design.
- Check the number. Confirm the check digit and that the scanner shows exactly the characters you expected.
- Check size, margins and colours. Compare the print with the standard size, look for cropped quiet zones and make sure the bars are dark on light.
- Check the scanner's settings. Make sure the symbology is switched on and the length settings allow your barcode.
- Print a new proof. Change one thing at a time so you know which fix worked.
For QR codes, see QR code not scanning.