The printed barcode can have different resolutions, including:

High resolution:
Means high density. Define the thinnest line width to be 6 mil (0.15 mm).

Medium resolution:
Means medium density. Define the thinnest line width to be 10 mil (0.25 mm).

Low resolution:
Means low density. Define the thinnest line width to be 13 mil (0.33 mm).

* 1 inch = 1000 mil =25.4 mm

The number of barcode characters at high resoluiton is higher than at low resolution. This is because of high resolution barcode means higher density.

High resolution = More characters per inch
Low resolution = Less characters per inch