Developed in the mid-1970s, Code 39 is the first alphanumeric barcode symbology developed. Sometimes also called Code 3 of 9, USS Code 39, USD-3, Alpha39, or Type 39, this 1D barcode remains popular today—it’s valued for its simplicity and flexibility in tracking inventory in industries such as electronics, healthcare, and government.
About Code 39
Code 39 is a discrete, self-checking, and variable-length code that’s linear—that is, it’s read by scanning across its bars.
- Discrete code: Each character can stand alone and can be decoded independently. The characters are separated by inter-character gaps that contain no information.
- Self-checking: Can detect printing errors and prevent misreads or omissions.
- Variable-length: Has no limit to the number of characters that can be encoded—other than those imposed by the size of the label.
Structure
How does Code 39 work? Code 39 uses all 26 uppercase alphabetical characters, 10 numeric characters—0 to 9—and 6 special characters:
- Percent sign (%)
- Plus sign (+)
- Dollar sign ($)
- Slash mark (/)
- Period (.)
- Hyphen (-)
Each character in a Code 39 barcode is encoded as 9 elements—5 bars and 4 spaces—of which exactly 3 are wide and 6 are narrow, giving the symbology its name.
Code 39 can also use start and stop characters—although they’re not required—and, as their name implies, tell the scanner where the information begins and ends. An asterisk (*) is most commonly used as the start and stop character.
Pros and Cons
Is Code 39 right for your application? The classic code offers distinct advantages, including:
- Versatility: Uses both letters and numbers, making it well-suited to a variety of applications.
- Compatibility: Most barcode scanners and systems support Code 39, making it easy to integrate across platforms.
- Self-checking: Reduces scanning errors without requiring a check digit.
- Human-readable: Code 39 encodes alphanumeric characters that are readable without a scanner, which is useful in applications that require manual verification.
While there are benefits to using Code 39, there are also some drawbacks, such as:
- Low-density: Takes up more space than other, more compact codes, making it less than ideal for small labels.
- Limited characters: Since Code 39 only uses 43 characters—26 alphabetical, 10 numeric, and 6 special—its versatility is restricted.
- Errors: While Code 39 is self-checking, poor print quality, smudges, or tears can cause scanning issues.
Code 39 vs Code 128
Code 128 is a variable-length, self-checking barcode developed in the early 1980s, specifically designed to address the shortcomings of established symbologies, like Code 39.
Code 128 supports all 128 ASCII characters—hence its name—which include upper- and lower-case letters, numbers, symbols, and control characters. Each character in Code 128 is represented by six elements, which offers greater density than Code 39, meaning it can encode more data in a smaller space. Code 128 also features a mandatory check digit to ensure accurate scanning.
Applications that require encoding a large amount of information in small spaces and demand high data accuracy are optimal uses for Code 128 barcodes.
How to Identify Code 39
An easy way to tell if you’re looking at a Code 39 barcode is to look at the bar patterns representing the start and stop—the first and last five bars of the code. In a Code 39 barcode, the bars and spaces representing the start and stop characters will match:
- Narrow bar
- Wide space
- Narrow bar
- Narrow space
- Wide bar
- Narrow space
- Wide bar
- Narrow space
- Narrow bar
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