Why won't my barcode scan? A troubleshooting checklist

When a barcode won't scan, the fault is in the label, the scanner or the data behind the code. Work through these checks in order; the first shows which of the three you have.

How to test a barcode against a known-good code

Scan a code you know reads, such as a manufacturer's barcode on a best seller, then the failing label.

• Both fail. The scanner or its settings are at fault. Skip to the scanner section.
• Only the label fails. Continue with the print checks.
• Both read, but the stock system shows nothing or the wrong product. The data is wrong. Skip to the check digit section.

Most scanners type like a keyboard, so scan into a plain text editor and compare what appears with the digits under the bars. Then try a second copy of the label. If one copy reads, the first is damaged. If every copy fails, the cause is in the file or the printer.

Blurry barcode: soft edges merge the bars

Blurred edges fill in the narrow spaces between bars, and the pattern stops decoding. The GS1 US barcode placement and printing guidelines call for high-resolution artwork and printing.

• Resolution. Draft mode gives ragged edges. Print at normal or best quality.
• A dirty thermal printhead. A white line through every label in the same place means debris on the head. Clean it as the manual describes.
• Heat and ribbon. Too much heat or darkness spreads the bars, and too little leaves them pale and broken. A ribbon that does not suit the label material smears. Change one setting at a time.
• Ink bleed. Inkjet ink spreads on uncoated paper, so use labels made for your printer.
• A scaled image. A barcode pasted as a picture or screenshot and then resized loses its sharp edges. GS1 US advises against shrinking or enlarging barcode art. Re-create the code at the size you need.

The free shelf label maker generates each code from the SKU or product number, so there is no image to resize.

Distorted barcode: stretched, curved or wrinkled

• Stretched. Dragging one side of a code in a design program changes the bar proportions. GS1 US notes that a UPC symbol has a fixed relationship between height and width, so both must change together. Regenerate rather than resize.
• Curved. On a narrow bottle, a code wrapped around the curve bends its ends out of view. GS1 has separate placement guidance for curved items; turning the code so its bars run around the item usually helps.
• Wrinkled. A label over a seam or a dusty surface puckers across the bars. GS1 US stresses a smooth printed surface, so apply labels to a clean, flat area.

What colors can a barcode be?

GS1 US says black bars on a white background work best. Bars must be dark, such as black, dark blue or dark green, in a single ink. Avoid red and reddish colors like brown, because scanning lasers use red light, which makes red bars disappear. Spaces and margins need a light background.

Low contrast can come from gray bars on low toner, faded thermal labels or dark kraft paper.

Leave a clear quiet zone

The quiet zone, the blank margin left and right of the symbol, tells the scanner where the code starts and stops. Text, a price, a border or the label edge inside it can stop the read. The Excel barcode guide covers this on spreadsheet labels.

Too small or a truncated barcode

Shrinking a symbol narrows its thinnest bars until the printer cannot place them cleanly. Use a bigger label or a shorter code. Code 128 grows wider with every character, so a short SKU makes a smaller symbol.

A truncated code has had its height cut to fit. GS1 US recommends printing at full height, because truncation can cause incorrect scanning.

Damaged, glossy or laminated labels

Scuffs, tears, marker ink and sun fading break the pattern. Glossy stock, laminate and shrink wrap reflect the scanner's light, so a label may read from one angle only. Tilt the scanner a little instead of holding it square. If you laminate shelf labels, test one first; matte finishes reflect less.

Barcode scanner settings and the wrong symbology

• Code type. A laser scanner reads linear codes only, not QR codes or Data Matrix, as the 1D and 2D barcode guide explains. Some ship with certain symbologies off; the manual's configuration codes turn them on.
• Suffix. If digits appear but the form does not submit, set the scanner to add an Enter after each scan.
• Keyboard layout. A scanner set to another keyboard language types wrong symbols, which the text editor test reveals.
• Connection. Try another USB port, or check that a Bluetooth scanner is charged and paired. The barcode inventory setup guide compares scanner types.

Bad data: the barcode check digit and the product record

If the text editor shows the right number but the stock system cannot find it, check the data.

• Check digit. UPC-A and EAN-13 numbers end in a digit calculated from the others, so one mistyped digit shows up. Test a number with the GS1 US check digit calculator.
• Leading zeros. Spreadsheets drop them from numbers, and a UPC-A has a 13-digit form with a zero in front. Store codes as text.
• The wrong record. The number may be saved on another product, or shared by two.

In Headoffis, a product's optional barcode field rejects a wrong check digit and keeps leading zeros, and a UPC-A read in its 13-digit form still finds the product.

Reprint or replace?

• One copy fails: reprint that label.
• Every copy fails: fix the file or printer, regenerate, then reprint.
• Known-good codes fail: fix the scanner settings, or replace a laser model if you need 2D codes.
• The data is wrong: correct the product record, not the label.
• A manufacturer's code fails: key the number by hand and tell the supplier.

Test-scan every new label batch

1. Print one test sheet on the printer and label stock you will use, at 100% scale.
2. Scan every label into the stock system and confirm the right product appears.
3. Repeat after changing the printer, ribbon, label stock or design.
4. Keep a known-good label by the counter for the first check above.

A barcode verifier measures print quality against ISO/IEC 15416, the standard for linear symbols. GS1 Austria's verification service, for example, checks structure, check digit, dimensions and print quality against it and the GS1 specifications. It matters most for products you make and sell through other retailers.

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