First off, what is a Quiet Zone? This is a blank area or margin on either end of a lineal barcode (such as Code 39 and Code 128) where no text, graphics or any other print should appear. That empty space tells a barcode scanner where the barcode begins and ends; it also makes sure the reader doesn’t pick up information that isn’t pertinent to the barcode. No signal is created by a scanner in that blank space and thus the reason for it to be called a “quiet zone.”
The general sizing rule for a minimal quiet zone (QZ) is 10 times the width of the narrowest bar (aka the “X” dimension) in a barcode or 0.25 inch, whichever is greater. A common reason for barcodes to fail is because of inadequate quiet zones that confuse the barcodes with other print. If that margin isn’t big enough, the barcode may be unreadable—at least in one direction. In this case, bigger is better and therefore extra space on either end of the barcode is always preferred.
So getting back to that #2 pencil…It is simple, easy and fascinating that all you need to do is place a pencil on either end of the bar code symbol. If you see white space on both sides of the pencil, then your barcode will scan, but be sure to check both ends (quiet zones) of the barcode symbol.
Quiet zones for two dimensional (2D) barcodes are calculated differently. The popular QR Code that is being used in marketing materials recommends a white space of 5 times the size of a module (that is the size of one of the black squares within the code) and the QZ needs to be the same on all four sides of the code. For Datamatrix, a white space of 2 times the size of a module should be used—again on all four sides.
If you are ever in a store and the checkout clerk is having trouble scanning your merchandise, you might want to take a quick look at the barcode to see if you spot a quiet zone problem. Aside from poor print quality, an insufficient quiet zone could well be the culprit and you would get the chance to demonstrate your barcode expertise!