​​What Is Code 39?

​​Also called “Code 3 of 9” or “Alpha39,” Code 39 is a 1D barcode symbology used for tracking inventory, parts, and equipment across industrial, military, healthcare, and electronics applications.  

​Code 39 was the first barcode to encode both numbers and letters, and it supports variable-length alphanumeric characters. It is self-checking, so a separate check digit isn’t required (though recommended). Code 39 is valued for its simplicity, flexibility, and continued usefulness in non-retail environments.

​​Specifications: A Code 39 barcode is structured with the following key elements:

• ​Start/end characters – Mark the beginning and end of the barcode for the scanner, typically represented as * in regular fonts.
• ​Numeric encoding – Each number (0-9) has its own designation for encoding. Numbers 1-10 are represented directly.
• ​Letter encoding – Letters are assigned numeric values using special designations:
  • ​A–J: “Letters” designation + numeric value (1–10)
  • ​K–T: “Letters +10” designation + numeric value (K = Letters +10 + 1 → 11th letter)
  • ​U–Z: “Letters +20” designation + numeric value

​Advantages: The use of both letters and numbers makes Code 39 highly versatile. It is also self-checking, so it does not require a check digit. 

​Disadvantages: Limited to a maximum of 43 characters, Code 39’s method of assigning numeric values to letters also restricts versatility and prevents encoding other characters.

​Encoding type: Partial alphanumeric ▪ Format: Wide/narrow ▪ Check Digit: Optional

​Typical usage: Military & automotive

​Related barcodes:
Code 93 – A more compact version of Code 39.
Extended Code 39 – Encodes all ASCII characters using combinations of Code 39 symbols.