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Printing Bar Codes

The Design

The design and printing of any bar code requires the designer to understand fundamental concepts of bar codes, and printing systems.  Although all bar codes differ, some significantly, the basic design and printing concepts are very similar.

From a design standpoint, the size of a bar code is often the most important and contentious characteristic.   Existing labels, product packaging, and forms are often short on physical real estate required for successful bar code scanning.   Even when there is sufficient room, most people feel that aesthetics is more important than the bar code so, in an effort to reduce the amount of real estate required, designers often unknowingly introduce printing errors. This decreases scanning performance, and often generates unreadable bar codes. 

Printing Bar Codes

In general, any printer that can print a graphic image or picture can print a bar code.   However, it is not quite as simple as opening up a labeling software package and clicking with your mouse.

Many printing variables affect bar code print quality.  These variables include the type of printer and depending on that, the label stock; the printer's heat settings, the type of toner used; the type of ribbon used; how often the ribbon is changed; and more. Once the appropriate variables are understood, and specified, printing bar codes becomes much simpler.

Bar Code Size

Most designers try to make the bar code as small as possible even when there is enough space for a larger symbol.  Typically, to reduce the size of a bar code, a smaller   'X' dimension is used. Although picking a small 'X' dimension will reduce overall real estate requirements, smaller 'X' dimensions require higher resolution printers, and sometimes require high density scanning equipment capable of scanning small 'X' dimension symbols. In addition, decode performance can suffer.  Sometimes a different symbology can take up less space but most application standards do not allow the selection of an alternate symbology.

All bar code application standards specify the minimum allowable 'X' dimension allowed. Typical 'X' dimensions for both linear and 2D bar codes are 15, 10, and 6.6 mil (.01, or .00666 inches). Although an application developer might want to print a 10 mil code, whether or not a printer is capable, depends on several factors. The two most important factors are printer resolution, and ink spread.

Printer Resolution

A printers resolution is simply how many dots it can print in an inch (or mm). This resolution is referred to as DPI (Dots Per Inch).  Most laser printers today are capable of 300-1200 DPI, while the average ink jet prints at 360, or 720 DPI.  Thermal transfer printers typically have resolutions from 200 to 600 DPI. A printer's resolution, and output quality, determine the 'X' dimensions that are available for a specific printer.

The possible X' dimensions for a specific printer are determined by the following formula:

X = N / DPI
Where:
X = The X dimension
N = Number of dots per module (or X dimension)
DPI = The printer's resolution

Based on this formula, some of the possible 'X' dimensions for a 300 DPI printer might be:

N / 300 1 / 300 2 / 300 3 / 300
X mil 3.3 mil 6.6 mil 10 mil

 

The following table lists a number of printer technologies, and typical 'X' dimensions in mils for each technology:

Printer Technology DPI Typical Application Min 'X' Dim Other 'X' Dim
Thermal Transfer and Thermal Direct 200 Labeling 5
10 15 20 25 30
Fax 200 Short Documents 5
10 15 20 25 30
High Speed Printers 240 Mailing and Billing 8.33
12.50 16.66 20.83 25.00 30.00
Desktop Laser 300 Office Documents 6.66
10.00 13.33 16.66 20.00 23.33
Ink Jet 360 Home / Office Documents 8.33
11.11 13.88 16.66 19.44 22.22
Desktop Laser 600 Office Documents 5.00
6.666 8.333 10.00 11.66 13.33
Ink Jet 720 Home / Office Documents 4.167
5.555 6.940 8.333 9.720 11.11
Network / Desktop Laser 1200 Office Documents 2.50
3.333 4.166 5.000 5.833 6.666
High Resolution Ink Jet 1440 Home / Office Documents 3.42
4.166 4.866 5.555 6.250 6.940

NOTE: The selected 'X' dimension for any application must also consider the scanning equipment.  Typical scanners today can read anywhere from 6.6 mil code and up.  High density scanners are also available with capabilities ranging from 4 mil codes and up. The 'X' dimensions for each printer are NOT limited to those in the table above.