Free Code 128 barcode generator.

Type

Linear (1D), continuous, variable length, reads in both directions

Specification

ISO/IEC 15417; USS Code 128 (Uniform Symbology Specification) is identical

Character set

ASCII 0–127; bytes 128–255 (Latin-1) through FNC4

Code sets

A: ASCII 0–95, control characters
B: ASCII 32–127, lower case
C: digit pairs 00–99

Symbol character

11 modules: 3 bars, 3 spaces, each 1–4 modules; stop 13 modules

Symbol width

11 modules per character plus 35 for start, check and stop

Check character

Mandatory, modulo 103; not printed, not output by the scanner

Module width (X)

At least 0.19 mm (TEC-IT); label specifications set their own

Quiet zone

10X left and right, and at least 6.35 mm (¼ in) per TEC-IT

Length

Variable; the 48-character limit belongs to GS1-128

The generator picks the start character and code sets that need the fewest symbol characters. Code set B takes the letters and hyphens; code set C stores the closing digits as the pairs 12 and 34.

3041 = 29 × 103 + 54, so the check value is 54. The check character sits before the stop.

Thirteen characters of 11 modules plus the 13-module stop make 156 modules. At 0.254 mm per module that is 39.6 mm, plus 6.35 mm of quiet zone per side.

• Module width. At least 0.19 mm per TEC-IT's reference; TEC-IT's Code 128 templates set 0.254–0.700 mm where they fix it. Choose whole printer dots, above all on low-resolution thermal-transfer printers.
• Quiet zone. 10 modules on each side, but no less than 6.35 mm: at 0.339 mm, 10 modules are only 3.39 mm.
• Height. TEC-IT's reference sets none for Code 128; follow your label specification. TEC-IT's templates use 13 mm for the Caterpillar part number and 20 mm for the VDA 4994 A5 license plate.
• Bar gain. Compensate ink spread with bar width reduction. TEC-IT's sample values: about 100 µm for flexographic, 50 µm for intaglio, 30 µm for offset printing.
• Verification. Grade print quality with an ISO/IEC 15416 verifier, the method the GS1 General Specifications name for Code 128.

TEC-IT's Galia and Odette OTL 3 templates use 0.339 mm (about 4 dots at 300 dpi), its Ford GTL templates 0.423 mm (about 5 dots).

• Encoding GS1 data as plain Code 128. Without the function character FNC1 after the start character, a symbol is never GS1-128, so (01) and the digits arrive as plain text. Use the GS1-128 generator and leave out the parentheses.
• Fixing code set B for long numbers. Each digit then takes a full character: an 18-digit serial number needs 233 modules instead of 134. Let the encoder switch to code set C unless a specification fixes the set.
• Squeezing long data into a fixed box. The module width shrinks as the data grows and can drop below 0.19 mm. Shorten the data or use Data Matrix.
• Resizing or compressing the image. Scaling by a non-integer factor can give bars of the same width different dot counts, distorting Code 128's four bar widths. Generate the image at its final size and save it as PNG, not JPG.
• Appending a check digit by hand. The generator adds the mod 103 check character itself; an extra digit becomes data, and the scanner outputs it.