In barcode technology, the X dimension is the narrowest part of a barcode's symbology.
The X dimension is used to determine a barcode's density, which is the amount of information that can be captured in a barcode within a specific amount of space. Other elements of a bar code are expressed as multiples of the X dimension. For instance, to ensure accurate scanning, most bar codes have a quiet zone whose width is 10X, or ten times the bar code's X dimension. In general, the greater the X dimension, the easier it is to scan a bar code.