Code 39 Extended
Code 39 with escape sequences that map the full ASCII set onto the 43-character base alphabet.
Code 39 Extended Specification
| Character set | Full ASCII 0-127 via two-character shift sequences over the base 43-character set |
| Data length | Variable; non-base characters consume two code positions each |
| Check digit | Optional Mod 43 (computed over the transmitted ASCII data, not the shift pairs) |
| Density | ≈5-9 base characters per inch; effectively halves for lowercase-heavy data |
| Module width (X-dimension) | 0.19-0.50 mm typical |
| Print ratio | Wide:narrow ratio 2:1 to 3:1 |
| Magnification | Scales with X-dimension and ratio |
| Quiet zone | 10X on each side |
| Standard | ISO/IEC 16388 (extended interpretation); AIM USS-39 |
| Origin | David Allais and Ray Stevens, Intermec (extension popularized in the 1980s), 1974 |
| Sample data | Code39 Ext! |
Try It: Generate a Code 39 Extended Barcode
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What Is Code 39 Extended?
Code 39 Extended (also called Full ASCII Code 39) overlays a convention on plain Code 39: lowercase letters and the remaining ASCII characters are encoded as two-character sequences built from the four "zero-shift" characters $ / + % followed by a base character. For example, lowercase a is encoded as +A. A compliant scanner strips the shift pair and transmits the single resulting character, so the host system receives ordinary ASCII.
The cost is width: any character outside the base 43 takes double the space, so a fully lowercase string becomes about twice as wide as its Code 128 equivalent. Extended Code 39 persists in older systems that predate Code 128 adoption and in environments where a single symbology must handle arbitrary keyboard input. New deployments should generally prefer Code 128.
Common Applications
- Legacy systems requiring full keyboard ASCII in Code 39
- Mixed alphanumeric data in Code 39-based supply chains
- Applications that cannot change symbology but receive arbitrary text
Related Barcode Types
The classic self-checking alphanumeric barcode: 43 characters, simple structure, still everywhere in industry.
A high-density, variable-length linear barcode that encodes all 128 ASCII characters, and the backbone symbology of modern logistics.
Code 39 carrying the Health Industry Bar Code supplier labeling structure — the legacy healthcare marking standard.
Code 39 Extended FAQ
Will every Code 39 scanner read extended characters correctly?
Most modern scanners enable Full ASCII translation by default or by a config toggle, but it is the weakest compatibility point of the format: a scanner without the mode active will transmit the raw shift pairs (+A instead of a). For critical flows, verify scanner configuration or move to Code 128.
How much wider is Extended Code 39 than Code 128 for mixed-case text?
Roughly 2.5-3× for lowercase-heavy strings: each lowercase letter costs two 9-element characters plus a separator versus one 11-module character in Code 128. That width difference is the main reason Code 128 displaced it wherever label space matters.