Code 128 Barcode Generator

Code 128 is a linear barcode that holds all 128 ASCII characters: capitals, lower case, digits, punctuation and control characters. It is compact for its range, so warehouses, carriers, labs and factories use it wherever a code carries letters as well as numbers.

It reads left to right as a quiet zone, a start character, the data, a check character, a stop character and a second quiet zone. Every symbol is 11 modules wide, made of 3 bars and 3 spaces from 1 to 4 modules each; the stop is 13 modules with its final bar. The quiet zones are 10 modules each.

Because each symbol always takes 11 modules, the width of the barcode follows directly from the number of symbols and the module width you choose: this generator prints both.

Code 128 has three code sets that share the same 107 patterns. Set A covers capitals, digits, punctuation and the control characters such as Tab and Enter. Set B covers capitals, lower case, digits and punctuation. Set C packs two digits into each symbol, 00 to 99.

A barcode can start in any set and switch with a Code A, Code B or Code C symbol, or Shift for one character between A and B. Set C pays off for a run of four or more digits at the start or end, and six or more in the middle. The example X00Y stays in set B in 7 symbols; 098x1234567y23 takes 16 symbols with set C for the middle digits.

Auto in this generator works out the shortest mix for your data every time, and the width table shows what holding a single set would cost.

The check character is a weighted sum mod 103. Take the start character’s value, add each following symbol’s value times its position (the first symbol after the start is position 1), and divide by 103: the remainder is the value of the check character, printed just before the stop.

For PJJ123C in set A: start 103, then 48 × 1, 42 × 2, 42 × 3, 17 × 4, 18 × 5, 19 × 6 and 35 × 7 add up to 878, and 878 mod 103 is 54. The scanner does the same sum, and a code whose check character matches reads; that is how the symbology catches a misread bar.

The check character is part of the bars only. Scanners don’t send it, and the printed line under the barcode shows your data without it.

All 107 values with their meaning in sets A, B and C and their bar and space widths. Values 0 to 95 are characters in sets A and B, 0 to 99 are digit pairs in set C, 96 to 102 are function characters in sets A and B, and 100 to 102 in set C, 103 to 105 are the three starts and 106 is the stop.

GS1-128 is Code 128 with GS1 rules: an FNC1 right after the start, then application identifiers such as (00) for an SSCC, (01) for a GTIN, (10) for a lot and (17) for an expiry date. A variable-length field with another field after it ends with an FNC1, which scanners pass on as the GS character.

GS1 sets the limits for logistics labels: at most 48 data characters, a symbol up to 165.10 mm wide with its quiet zones, and a module from 0.495 mm. For your own part numbers, bins and assets, plain Code 128 is the right choice; for cartons and pallets that travel between companies, choose GS1-128.

The module, the narrowest bar, sets the size of the whole barcode. 0.25 to 0.5 mm suits most labels; 0.33 mm is about 13 mil. Below 7.5 mil many scanners read the bars poorly, and the generator says so.

A thermal printer at 203 dpi prints dots of 0.125 mm, so a 0.33 mm module becomes 3 dots, 0.375 mm. Choosing the printer in the generator rounds the module to whole dots before you print, which keeps every bar the same width. Keep the 10-module quiet zone clear on both sides, and make the bars at least 6.35 mm tall, or 15 percent of the code’s length when that is more.

In Word or Excel, a Code 128 font needs its start, check and stop characters added by a formula. A PNG or SVG from this generator already has them: insert it like any picture, at 100 percent.