Bar Code Design

The following charts will help when designing forms with bar codes that will be read by imaging systems from Acordex. Allow a space as shown in the charts. Code 39 can include letters and numbers, code 25 is numbers only (each character is 0 thru 9). The quiet zone must be on both sides of the bar code.

Code 39 (3 of 9)

Minimum space when using a dot matrix printer:

# characters of data	length (in)	height (in)
(don't count start/stop)	(including quiet zone)
4	1.2	0.2
6	1.6	0.3
8	2.1	0.5
10	2.5	0.6
12	3.0	0.7
14	3.4	0.8

Spec:
quiet zone: 1/10" or 10x the width of a narrow bar, whichever is larger
quiet zone for optimal hand scanning: 1/4"
aspect ratio: 4:1
highest density: 9.4 characters/in
 
For dot matrix or line printers:
quiet zone: 3/16" minimum
aspect ratio: 4:1 (tolerates 10° of skew)
density: 4.5 characters/in

Code 25 (Interleaved 2 of 5)

Minimum space when using a dot matrix printer:

# characters of data	length (in)	height (in)
(don't count start/stop)	(including quiet zone)
4	0.9	0.2
6	1.2	0.3
8	1.5	0.3
10	1.8	0.4
12	2.1	0.4
14	2.4	0.5

For dot matrix or line printers:
quiet zone: 3/16" minimum
aspect ratio: 4:1
density: 6.5 characters/in

Pre-printed Bar Codes

Bar code stickers that have been pre-printed on a printing press or laser-printer can include bar codes of higher density than dot-matrix printers. This is simply because they print at higher resolution and each bar can be printed smaller.

The limit for these bar codes is the planned resolution setting for the scanner. For most high volume document applications, this is 200 dpi (.005 in). This means a narrow bar should be at least .0075 in. (min) .01 (preferred), and the thick bars should be 2x to 3x as wide.

If a black bar is at or smaller than 1/200 of an inch, the scanner will miss it, or will miss the adjacent white bar. this makes the bar code unreadable. Ensure that a narrow bar is wider than planned resolution setting for the scanner.

Always test bar code stickers before printing your volume run!

Check Digits for Bar Code 25

The Bar Code 25 can have a check digit which uses a weighted Modulo 10 scheme. The check digit is the last character in the bar code. Since Bar Code 25 must always have an even number of digits, the leftmost character may need to be a zero when the check digit is added. The standard check digit is calculated by assigning alternating 3,1,3,1.. weights to respective data digits. These weights are then multiplied by their respective data digits and the products are summed. The check digit is the digit needed to be added to the sum to make it an even multiple of 10. An example would be if the sum of the products was 37, the check digit would be 3.

Here is another explanation of how to calculate the check digit. Starting with the left most character, multiply every other digit (odd positions) by 3 and sum the results with the values of the even positions. (The check digit is always an even position so it is never multiplied by 3.) The sum should be a multiple of 10. To compute the check digit for printing a bar code, perform the summing operation above without the check digit, do a modulo 10 on the result, and subtract the value from 10 to yield the check digit. (If you start with an even number of digits, make sure you add a leading zero before you do the calculation.)

Note: When printing bar codes the check digit should NOT be printed in the human readable number above the bar code. The user does not enter the check digit in the event that the bar code cannot be automatically read and would be confused by the extra digit that is not part of the document number.

For example if the number to be bar coded was:
1234567
then the sum would be:
(1*3) + (2*1) + (3*3) + (4*1) + (5*3) + (6*1) + (7*3) =
3 + 2 + 9 + 4 + 15 + 6 + 21 = 60
remainder of 60/10 = 0
check digit = 10 - 0 = 0
barcoded number = 12345670

Another example if the number to be bar coded was:
83456
(8*3) + (3*1) + (4*3) + (5*1) + (6*3) =
24 + 3 + 12 + 5 + 18 = 62
remainder of 62/10 = 2
check digit = 10 - 2 = 8
barcoded number = 834568

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