Barcode Not Scanning? A Checklist From Most to Least Likely

First, find out which side is failing

Two quick tests split the problem in half.

• Scan a known-good barcode, such as the UPC on any packaged product from a store. If the scanner reads that but not yours, the problem is your barcode or the scanner's setting for that barcode type. If it reads nothing at all, check the cable, power and connection first.
• Scan your barcode with a second device, such as a phone app. If nothing reads it, start with the print (items 4 to 8). If the phone reads it but the scanner doesn't, start with the scanner (items 1 to 3), but don't clear the print yet: a phone forgives low contrast and red ink that a checkout scanner won't, according to the GS1 2D Barcode Colour & Quality Guide.

Also notice whether the scanner beeps. A beep means it decoded something. If the beep comes but the wrong text appears, or nothing appears, skip to items 9 and 10.

Scanner-side causes

1. The scanner can't read that kind of code

Laser scanners and linear imagers read a single line across the code, so they only read 1D barcodes. The GS1 General Specifications state plainly that linear imagers, like laser scanners, can't scan 2D barcodes such as QR codes. Laser scanners also can't read a barcode shown on a phone screen (Zebra).

Fix: use a 2D area imager for QR codes and screens. See how barcode scanners work for the differences.

2. That barcode type is switched off or length-limited

Many scanners ship with only some symbologies turned on. Zebra's LS2208 reference guide, for example, lists Codabar, Code 93 and GS1 DataBar as disabled by default, and sets Interleaved 2 of 5 to read only 14- or 44-digit codes. A Codabar library label or a 10-digit ITF code is simply ignored until you change the setting.

Fix: look up the barcode type in your scanner's reference guide and scan the programming barcode that enables it. For length-limited types, set the allowed length to match your data.

3. The aim, angle or distance is off

A laser's scan line has to cross every bar and space, including the blank margins on both ends. Zebra's LS2208 guide also warns against aiming straight on: light bouncing directly back (specular reflection) can block decoding, so tilt the scanner slightly.

Distance matters too. The same guide lists a 100% UPC as readable from contact out to 17 in., but a fine 5 mil Code 39 only from about 2.5 to 6 in. Small barcodes need you to move closer.

Print-side causes

4. The quiet zone is crowded

The quiet zone is the blank margin on each side of the bars, and the scanner needs it to find where the symbol starts and stops. Minimums are counted in modules (X): 9X on each side of a UPC-A, 11X left and 7X right on an EAN-13, and 10X on each side of Code 128 and ITF-14. A label edge, border, logo or line of text inside that space is a classic cause of no-reads.

Fix: move the other elements, not the barcode. Zebra suggests at least 1/8 in. (3.2 mm) between a barcode and other print or the label edge (Zebra).

5. It's too small, or the image was resized

A barcode below its minimum size, or one stretched or squeezed after export, has bars that are too thin or uneven. On a label printer, trouble also starts when the narrowest bar isn't a whole number of printer dots: at 203 dpi each dot is 0.125 mm, so a 100% UPC would need 2.64 dots per module, and the printer has to round.

Fix: regenerate the barcode at its final size in the generator instead of scaling an image, and size it to whole printer dots. The printing guide linked at the end of this page works through the math.

6. The print is too dark, too light or streaked

On thermal printers, too much heat spreads the bars into the spaces; GS1 notes that raising printhead temperature also widens bars. Too little heat leaves broken bars. Zebra recommends the lowest darkness and speed that give a clean result.

Thin white lines running the length of every label point to a dirty printhead or damaged heating elements (Zebra). If a line runs through the middle of a bar, the scanner may see two thin bars instead of one.

Fix: clean the printhead, lower darkness, and replace the printhead if the lines stay. On office printers, check for low toner, smearing or a "draft" quality setting.

7. The colors, glare or background are wrong

Checkout scanners use red light, so red, orange and reddish-brown bars look the same as the background and disappear. Dark bars on a dark background fail for the same reason. Glossy laminate, foil and clear film add glare or let the contents show through.

Fix: print black, dark blue or dark green bars on a white or other light background. On clear or metallic packaging, GS1 recommends printing an opaque white area under the barcode first.

8. The label has faded, been damaged or wraps a tight curve

Direct thermal labels keep reacting to heat and light. Zebra notes they darken when overexposed until the barcode can't be read, which makes them a poor fit for long-term labels. Scratches, creases and a symbol wrapped around a narrow bottle can also hide bars.

Fix: reprint damaged labels, use thermal transfer labels for anything long-lived, and on tight curves rotate the barcode so the bars run around the curve. GS1's rule is that the barcode's ends shouldn't curve away more than 30 degrees.

It beeps, but the data is wrong

9. The number or check digit is wrong

UPC and EAN symbols must end in a correct check digit, which GS1 makes mandatory. If you typed digits from an old spreadsheet or swapped two numbers, the printed barcode may decode to the wrong product or not at all. GS1 also notes that verifiers don't check whether the human-readable digits match the bars, so a mismatch can slip through.

Fix: confirm the number with the check digit calculator and compare the decoded output with the digits printed under the bars.

10. The scan arrives garbled, short or in the wrong place

Many USB scanners, including the LS2208, act as a keyboard by default and type into whatever window has focus. Zebra's LS2208 guide lists settings for keyboard country layout, Caps Lock handling, an Enter or other suffix after each scan, and whether a UPC's check digit is sent. A wrong keyboard layout swaps characters, and Caps Lock can flip letter case.

Spreadsheets cause their own trouble. Excel strips leading zeros, shows long numbers in scientific notation, and rounds any digits after the 15th to zero (Microsoft Support), which corrupts an 18-digit SSCC. And in GS1-128, the parentheses around application identifiers appear only in the printed text, never in the scanned data.

Fix: format the receiving column as Text before you scan, set the scanner's keyboard layout and suffix to match your computer, and expect GS1-128 data without parentheses. More spreadsheet tips are in barcodes in Excel and Google Sheets.

Next step

Take one failing label and work down this list, changing one thing at a time. If the barcode itself turns out to be the problem, regenerate it at final size and run through the pre-print checklist in how to print barcodes that scan before you print a new batch.